Gamco Mathers Fund N-CSRS Certified semi-annual shareholder report (management investment company)

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM N-CSR

CERTIFIED SHAREHOLDER REPORT OF REGISTERED MANAGEMENT

INVESTMENT COMPANIES

Investment Company Act file number            811-01311            

                           The GAMCO Mathers Fund                          

(Exact name of registrant as specified in charter)

One Corporate Center

                         Rye, New York 10580-1422                            

(Address of principal executive offices) (Zip code)

Henry G. Van der Eb

Gabelli Funds, LLC

One Corporate Center

                         Rye, New York 10580-1422                            

(Name and address of agent for service)

Registrant’s telephone number, including area code:  1-800-422-3554

Date of fiscal year end:   December 31

Date of reporting period:   June 30, 2017

Form N-CSR is to be used by management investment companies to file reports with the Commission not later than 10 days after the transmission to stockholders of any report that is required to be transmitted to stockholders under Rule 30e-1 under the Investment Company Act of 1940 (17 CFR 270.30e-1). The Commission may use the information provided on Form N-CSR in its regulatory, disclosure review, inspection, and policymaking roles.

A registrant is required to disclose the information specified by Form N-CSR, and the Commission will make this information public. A registrant is not required to respond to the collection of information contained in Form N-CSR unless the Form displays a currently valid Office of Management and Budget (“OMB”) control number. Please direct comments concerning the accuracy of the information collection burden estimate and any suggestions for reducing the burden to Secretary, Securities and Exchange Commission, 450 Fifth Street, NW, Washington, DC 20549-0609. The OMB has reviewed this collection of information under the clearance requirements of 44 U.S.C. § 3507.

Item 1. Reports to Stockholders.

The Report to Shareholders is attached herewith.

GAMCO Mathers Fund   Semiannual Report — June 30, 2017   Henry G. Van der Eb, CFA Portfolio Manager

To Our Shareholders,

The Sarbanes-Oxley Act’s corporate governance regulations require a Fund’s principal executive and financial officers to certify the entire contents of the quarterly, semiannual, and annual shareholder reports in a filing with the Securities and Exchange Commission (the “SEC”). This certification covers the portfolio manager’s commentary and subjective opinions if they are attached to or a part of the financial statements.

Rather than ask our portfolio manager to eliminate his opinions and/or restrict his commentary to historical facts only, we separated his commentary from the financial statements and investment portfolio and sent it to you separately to ensure that its content is complete and unrestricted. Both the commentary and the financial statements, including the portfolio of investments, are also available on our website at www.gabelli.com.

We trust that you understand that our approach is an unintended consequence of the ever increasing regulatory requirements affecting public companies. We hope the specific certification requirements of these regulations will be modified as they relate to mutual funds, since investment companies have different corporate structures and objectives from other public companies.

GAMCO Mathers Fund

Disclosure of Fund Expenses (Unaudited)

For the Six Month Period from January 1, 2017 through June 30, 2017 Expense Table

We believe it is important for you to understand the impact of fees and expenses regarding your investment. All mutual funds have operating expenses. As a shareholder of a fund, you incur ongoing costs, which include costs for portfolio management, administrative services, and shareholder reports (like this one), among others. Operating expenses, which are deducted from a fund’s gross income, directly reduce the investment return of a fund. When a fund’s expenses are expressed as a percentage of its average net assets, this figure is known as the expense ratio. The following examples are intended to help you understand the ongoing costs (in dollars) of investing in your Fund and to compare these costs with those of other mutual funds. The examples are based on an investment of $1,000 made at the beginning of the period shown and held for the entire period.

The Expense Table below illustrates your Fund’s costs in two ways:

Actual Fund Return: This section provides information about actual account values and actual expenses. You may use this section to help you to estimate the actual expenses that you paid over the period after any fee waivers and expense reimbursements. The “Ending Account Value” shown is derived from the Fund’s actual return during the past six months, and the “Expenses Paid During Period” shows the dollar amount that would have been paid by an investor who started with $1,000 in the Fund. You may use this information, together with the amount you invested, to estimate the expenses that you paid over the period.

To do so, simply divide your account value by $1,000 (for example, an $8,600 account value divided by $1,000 = 8.6), then multiply the result by the number given for your Fund under the heading “Expenses Paid During Period” to estimate the expenses you paid during this period.

Hypothetical 5% Return: This section provides information about hypothetical account values and hypothetical expenses based on the Fund’s actual expense ratio. It assumes a hypothetical annualized return of 5% before expenses during the period shown. In this case –because the hypothetical return used is not the Fund’s actual return – the results do not apply to your investment and you cannot use the hypothetical account value and expense to estimate the actual ending account balance or expenses you paid for the period. This example is useful in making comparisons of the ongoing costs of investing in the Fund and other funds. To do so, compare this 5% hypothetical example with the 5% hypothetical examples that appear in shareholder reports of other funds.

Please note that the expenses shown in the table are meant to highlight your ongoing costs only and do not reflect any transactional costs such as sales charges (loads), redemption fees, or exchange fees, if any, which are described in the Prospectus. If these costs were applied to your account, your costs would be higher. Therefore, the 5% hypothetical return is useful in comparing ongoing costs only, and will not help you determine the relative total costs of owning different funds.

	Beginning Account Value 01/01/17	Ending Account Value 06/30/17		Annualized Expense Ratio		Expenses Paid During Period*
GAMCO Mathers Fund
Actual Fund Return
	$1,000.00		$   885.70		4.93%		$23.05
Hypothetical 5% Return
	$1,000.00		$1,000.35		4.93%		$24.45

* Expenses are equal to the Fund’s annualized expense ratio for the last six months multiplied by the average account value over the period, multiplied by the number of days in the most recent fiscal half year (181 days), then divided by 365.

2

Summary of Portfolio Holdings (Unaudited)

The following table presents portfolio holdings as a percent of net assets as of June 30, 2017:

GAMCO Mathers Fund – Long Positions
U.S. Treasury Bills	99.7	%
Other Assets and Liabilities (Net)	50.0	%

GAMCO Mathers Fund – Short Positions
Exchange Traded Funds	(43.0	)%
Retail	(3.3	)%
Beverages	(1.6	)%
Machinery	(1.1	)%
Electronics	(0.7	)%
	100.0	%

The Fund files a complete schedule of portfolio holdings with the Securities and Exchange Commission (the “SEC”) for the first and third quarters of each fiscal year on Form N-Q. Shareholders may obtain this information at www.gabelli.com or by calling the Fund at 800-GABELLI (800-422-3554). The Fund’s Form N-Q is available on the SEC’s website at www.sec.gov and may also be reviewed and copied at the SEC’s Public Reference Room in Washington, DC. Information on the operation of the Public Reference Room may be obtained by calling 800-SEC-0330.

Proxy Voting

The Fund files Form N-PX with its complete proxy voting record for the twelve months ended June 30, no later than August 31 of each year. A description of the Fund’s proxy voting policies, procedures, and how the Fund voted proxies relating to portfolio securities is available without charge, upon request, by (i) calling 800-GABELLI (800-422-3554); (ii) writing to The Gabelli Funds at One Corporate Center, Rye, NY 10580-1422; or (iii) visiting the SEC’s website at www.sec.gov.

3

GAMCO Mathers Fund

Schedule of Investments — June 30, 2017 (Unaudited)

Principal Amount			Cost		Market Value
		SHORT TERM OBLIGATIONS — 99.7%
		U.S. Treasury Bills — 99.7%
	$  9,782,000	U.S. Treasury Bills,
		0.766% to 0.886%†, 07/13/17(a)	$	9,779,117	$	9,779,907
		TOTAL INVESTMENTS — 99.7%	$	9,779,117		9,779,907
		SECURITIES SOLD SHORT — (49.7)%
		(Proceeds received $4,490,215)				(4,878,920	)
		Other Assets and Liabilities (Net) — 50.0%				4,912,113
		NET ASSETS — 100.0%			$	9,813,100
Shares			Proceeds		Market Value
		SECURITIES SOLD SHORT — (49.7)%
		Beverages — (1.6)%
	1,000	PepsiCo Inc.	$	106,718	$	115,490
	1,000	The Coca-Cola Co.		44,009		44,850
				150,727		160,340
		Electronics — (0.7)%
	2,000	Intel Corp.		74,958		67,480
		Exchange Traded Funds — (43.0)%
	10,000	Financial Select Sector SPDR Fund		246,815		246,700
	2,000	Industrial Select Sector SPDR Fund		117,097		136,220
	4,000	iShares Micro-Cap ETF		318,286		355,720
	6,000	iShares MSCI Emerging Markets ETF		218,487		248,340
	8,000	iShares MSCI Italy Capped ETF		205,995		222,400
	4,000	iShares MSCI Japan ETF		200,686		214,600
	2,000	iShares Russell 2000 ETF		248,150		281,840

Shares		Proceeds		Market Value
1,000	Powershares QQQ Trust Series 1	$	123,602	$	137,640
8,000	Real Estate Select Sector SPDR Fund		257,736		257,600
1,000	SPDR Dow Jones Industrial Average ETF Trust.		182,289		213,240
1,000	SPDR S&P 500 ETF Trust		236,007		241,800
1,000	SPDR S&P MidCap 400 ETF Trust		312,570		317,620
4,000	Technology Select Sector SPDR Fund		158,680		218,880
3,000	Utilities Select Sector SPDR Fund		144,677		155,880
5,000	Vanguard FTSE All-World ex-US ETF		225,855		250,150
5,000	Vanguard FTSE Europe ETF		245,835		275,700
2,000	Vanguard Total Stock Market ETF		243,626		248,900
8,000	WisdomTree India Earnings Fund		170,476		196,080
			3,856,869		4,219,310
	Machinery — (1.1)%
1,000	Caterpillar Inc.		94,648		107,460
	Retail — (3.3)%
2,000	Best Buy Co Inc.		119,189		114,660
1,000	Starbucks Corp.		53,229		58,310
2,000	Wal-Mart Stores Inc.		140,595		151,360
			313,013		324,330
	TOTAL SECURITIES SOLD SHORT(b)	$	4,490,215	$	4,878,920

(a) At June 30, 2017, $6,500,000 of the principal amount was pledged as collateral for securities sold short.

(b) At June 30, 2017, these proceeds are being held at Pershing LLC.

† Represents annualized yield at date of purchase.

See accompanying notes to financial statements.

4

GAMCO Mathers Fund

Statement of Assets and Liabilities

June 30, 2017 (Unaudited)

Assets:
Investments, at value (cost $9,779,117)	$	9,779,907
Cash		58,511
Deposit at brokers		4,894,560
Prepaid expenses		14,191
Total Assets		14,747,169
Liabilities:
Securities sold short, at value (proceeds $4,490,215)		4,878,920
Payable for Fund shares redeemed		5,852
Payable for investment advisory fees		8,096
Payable for distribution fees		2,024
Dividends payable on securities sold short		3,530
Other accrued expenses		35,647
Total Liabilities		4,934,069
Net Assets (applicable to 1,890,618 shares outstanding)	$	9,813,100
Net Assets Consist of:
Paid-in capital	$	16,989,744
Accumulated net investment loss		(227,742	)
Accumulated net realized loss on investments and securities sold short		(6,560,987	)
Net unrealized appreciation on investments		790
Net unrealized depreciation on securities sold short		(388,705	)
Net Assets	$	9,813,100
Shares of Beneficial Interest, each at $0.001 par value; unlimited number of shares authorized:
Net Asset Value, offering, and redemption price per share ($9,813,100 ÷ 1,890,618 shares outstanding)	$	5.19

Statement of Operations

For the Six Months Ended June 30, 2017 (Unaudited)

Investment Income:
Interest	$	33,597
Total Investment Income		33,597
Expenses:
Investment advisory fees		52,978
Distribution fees		13,245
Dividend expense on securities sold short		77,110
Trustees’ fees		26,282
Legal and audit fees		22,069
Service fees for securities sold short (see Note 2)		19,139
Shareholder communications expenses		16,575
Registration expenses		14,898
Shareholder services fees		11,354
Custodian fees		1,699
Interest expense		14
Miscellaneous expenses		5,976
Total Expenses		261,339
Net Investment Loss		(227,742	)
Net Realized and Unrealized Gain/(Loss) on Investments and Securities Sold Short:
Net realized gain on investments		471
Net realized loss on securities sold short		(1,178,921	)
Net realized loss on investments and securities sold short		(1,178,450	)
Net change in unrealized appreciation/depreciation:
on investments		790
on securities sold short		85,795
Net change in unrealized appreciation/depreciation on investments and securities sold short		86,585
Net Realized and Unrealized Loss on Investments and Securities Sold Short		(1,091,865	)
Net Decrease in Net Assets Resulting from Operations	$	(1,319,607	)

See accompanying notes to financial statements.

5

GAMCO Mathers Fund

Statement of Changes in Net Assets

	Six Months Ended June 30, 2017 (Unaudited)			Year Ended December 31, 2016
Operations:
Net investment loss		$    (227,742	)		$    (786,838	)
Net realized loss on investments and securities sold short		(1,178,450	)		(1,880,814	)
Net change in unrealized appreciation/depreciation on investments and securities sold short		86,585			(356,371	)
Net Decrease in Net Assets Resulting from Operations		(1,319,607	)		(3,024,023	)
Shares of Beneficial Interest Transactions:
Net increase/(decrease) in net assets from shares of beneficial interest transactions		(1,876,916	)		1,250,541
Redemption Fees		100			582
Net Decrease in Net Assets		(3,196,423	)		(1,772,900	)
Net Assets:
Beginning of year		13,009,523			14,782,423
End of period (including undistributed net investment income of $0 and $0, respectively)		$  9,813,100			$13,009,523

See accompanying notes to financial statements.

6

GAMCO Mathers Fund

Financial Highlights

Selected data for a share of beneficial interest outstanding throughout each period:

	Six Months Ended June 30, 2017 (Unaudited)			Year Ended December 31,
				2016				2015				2014				2013				2012
Operating Performance:
Net asset value, beginning of year		$   5.86			$	6.77			$	6.98			$	7.58			$	8.92			$	9.55
Net investment loss(a)		(0.12	)			(0.26	)			(0.33	)			(0.33	)			(0.31	)			(0.28	)
Net realized and unrealized gain/(loss) on investments and securities sold short		(0.55	)			(0.65	)			0.12				(0.27	)			(1.03	)			(0.35	)
Total from investment operations		(0.67	)			(0.91	)			(0.21	)			(0.60	)			(1.34	)			(0.63	)
Redemption Fees(a)		0.00	(b)			0.00	(b)			0.00	(b)			—				—				—
Net Asset Value, End of Period		$   5.19			$	5.86			$	6.77			$	6.98			$	7.58			$	8.92
Total return†		(11.43	)%			(13.44	)%			(3.01	)%			(7.92	)%			(15.02	)%			(6.60	)%
Ratios to Average Net Assets and Supplemental Data:
Net assets, end of period (in 000’s)		$ 9,813			$	13,010			$	14,782			$	14,335			$	11,223			$	20,809
Ratio of net investment loss to average net assets		(4.30	)%(c)			(3.99	)%			(4.81	)%			(4.51	)%			(3.73	)%			(3.04	)%
Ratio of operating expenses to average net assets(d)		4.93	%(c)			4.60	%(e)			4.84	%(f)			4.54	%			3.80	%			3.11	%
Portfolio turnover rate		0	%			0	%			0	%			513	%			0	%			3,328	%

† Total return represents aggregate total return of a hypothetical $1,000 investment at the beginning of the year and sold at the end of the period including reinvestment of distributions. Total return for a period of less than one year is not annualized.

(a) Per share data are calculated using the average shares outstanding method.

(b) Amount represents less than $0.005 per share.

(c) Annualized.

(d) The Fund incurred dividend expense and service fees on securities sold short. If these expenses and fees had not been incurred, the ratios of operating expenses to average net assets for the six months ended June 30, 2017 and the years ended December, 31, 2016, 2015, 2014, 2013, and 2012 would have been 3.12%, 2.24%, 2.61%, 2.82%, 2.79% and 2.62%, respectively.

(e) During the year ended December 31, 2016, the Fund received a one time reimbursement of custody expenses paid in prior years. Had such reimbursement been included in 2016, the expense ratio would have been 4.25%.

(f) The Fund received credits from a designated broker who agreed to pay certain Fund operating expenses. Had such payments not been made, the expense ratio for the year ended December 31, 2015 would have been 4.85%.

See accompanying notes to financial statements.

7

GAMCO Mathers Fund

Notes to Financial Statements (Unaudited)

1. Organization. GAMCO Mathers Fund was organized on June 17, 1999 as a Delaware statutory trust. The Fund commenced investment operations on October 1, 1999 as the successor to the Mathers Fund, Inc. (the “Mathers Fund”) which was organized on March 31, 1965 as a Maryland corporation. The Mathers Fund commenced investment operations on August 19, 1965. The Fund is a diversified open-end management investment company registered under the Investment Company Act of 1940, as amended (the “1940 Act”). The Fund seeks to achieve capital appreciation over the long term in various market conditions without excessive risk of capital loss.

2. Significant Accounting Policies. As an investment company, the Fund follows the investment company accounting and reporting guidance, which is part of U.S. generally accepted accounting principles (“GAAP”) that may require the use of management estimates and assumptions in the preparation of its financial statements. Actual results could differ from those estimates. The following is a summary of significant accounting policies followed by the Fund in the preparation of its financial statements.

Security Valuation. Portfolio securities listed or traded on a nationally recognized securities exchange or traded in the U.S. over-the-counter market for which market quotations are readily available are valued at the last quoted sale price or a market’s official closing price as of the close of business on the day the securities are being valued. If there were no sales that day, the security is valued at the average of the closing bid and asked prices or, if there were no asked prices quoted on that day, then the security is valued at the closing bid price on that day. If no bid or asked prices are quoted on such day, the security is valued at the most recently available price or, if the Board of Trustees (the “Board”) so determines, by such other method as the Board shall determine in good faith to reflect its fair market value. Portfolio securities traded on more than one national securities exchange or market are valued according to the broadest and most representative market, as determined by GAMCO Asset Management, Inc. (the “Adviser”).

Portfolio securities primarily traded on a foreign market are generally valued at the preceding closing values of such securities on the relevant market, but may be fair valued pursuant to procedures established by the Board if market conditions change significantly after the close of the foreign market, but prior to the close of business on the day the securities are being valued. Debt obligations for which market quotations are readily available are valued at the average of the latest bid and asked prices. If there were no asked prices quoted on such day, the security is valued using the closing bid price, unless the Board determines such amount does not reflect the securities’ fair value, in which case these securities will be fair valued as determined by the Board. Certain securities are valued principally using dealer quotations.

Securities and assets for which market quotations are not readily available are fair valued as determined by the Board. Fair valuation methodologies and procedures may include, but are not limited to: analysis and review of available financial and non-financial information about the company; comparisons with the valuation and changes in valuation of similar securities, including a comparison of foreign securities with the equivalent U.S. dollar value American Depositary Receipt securities at the close of the U.S. exchange; and evaluation of any other information that could be indicative of the value of the security.

8

GAMCO Mathers Fund

Notes to Financial Statements (Unaudited) (Continued)

The inputs and valuation techniques used to measure fair value of the Fund’s investments are summarized into three levels as described in the hierarchy below:

● Level 1 — quoted prices in active markets for identical securities;

● Level 2 — other significant observable inputs (including quoted prices for similar securities, interest rates, prepayment speeds, credit risk, etc.); and

● Level 3 — significant unobservable inputs (including the Board’s determinations as to the fair value of investments).

A financial instrument’s level within the fair value hierarchy is based on the lowest level of any input both individually and in the aggregate that is significant to the fair value measurement. The inputs or methodology used for valuing securities are not necessarily an indication of the risk associated with investing in those securities. The summary of the Fund’s investments in securities by inputs used to value the Fund’s investments as of June 30, 2017 is as follows:

	Valuation Inputs
	Level 1 Quoted Prices			Level 2 Other Significant Observable Inputs		Total Market Value at 6/30/17
INVESTMENTS IN SECURITIES:
ASSETS (Market Value):
Short Term Obligations:
U.S. Treasury Bills		—		$	9,779,907	$	9,779,907
TOTAL INVESTMENTS IN SECURITIES – ASSETS		—		$	9,779,907	$	9,779,907
LIABILITIES (Market Value):
Securities Sold Short (a)	$	(4,878,920	)		—	$	(4,878,920)
TOTAL INVESTMENTS IN SECURITIES – LIABILITIES	$	(4,878,920	)		—	$	(4,878,920)

(a) Please refer to the Schedule of Investments for the industry classifications of these portfolio holdings.

The Fund did not have transfers between Level 1 and Level 2 during the six months ended June 30, 2017. The Fund’s policy is to recognize transfers among Levels as of the beginning of the reporting period.

There were no Level 3 investments held at June 30, 2017 or December 31, 2016.

Additional Information to Evaluate Qualitative Information.

General. The Fund uses recognized industry pricing services — approved by the Board and unaffiliated with the Adviser — to value most of its securities, and uses broker quotes provided by market makers of securities not valued by these and other recognized pricing sources. Several different pricing feeds are received to value domestic equity securities, international equity securities, preferred equity securities, and fixed income securities. The data within these feeds are ultimately sourced from major stock exchanges and trading systems where these securities trade. The prices supplied by external sources are checked by obtaining quotations or actual transaction prices from market participants. If a price obtained from the pricing source is deemed unreliable, prices will be sought from another pricing service or from a broker/dealer that trades that security or similar securities.

Fair Valuation. Fair valued securities may be common or preferred equities, warrants, options, rights, or fixed income obligations. Where appropriate, Level 3 securities are those for which market quotations are not available, such as securities not traded for several days, or for which current bids are not available, or which

9

GAMCO Mathers Fund

Notes to Financial Statements (Unaudited) (Continued)

are restricted as to transfer. When fair valuing a security, factors to consider include recent prices of comparable securities that are publicly traded, reliable prices of securities not publicly traded, the use of valuation models, current analyst reports, valuing the income or cash flow of the issuer, or cost if the preceding factors do not apply. The circumstances of Level 3 securities are frequently monitored to determine if fair valuation measures continue to apply.

The Adviser reports quarterly to the Board the results of the application of fair valuation policies and procedures. These may include back testing the prices realized in subsequent trades of these fair valued securities to fair values previously recognized.

Repurchase Agreements. The Fund may enter into repurchase agreements with primary government securities dealers recognized by the Federal Reserve Board, with member banks of the Federal Reserve System, or with other brokers or dealers that meet credit guidelines established by the Adviser and reviewed by the Board. Under the terms of a typical repurchase agreement, the Fund takes possession of an underlying debt obligation subject to an obligation of the seller to repurchase, and the Fund to resell, the obligation at an agreed-upon price and time, thereby determining the yield during the Fund’s holding period. It is the policy of the Fund to receive and maintain securities as collateral whose market value is not less than their repurchase price. The Fund will make payment for such securities only upon physical delivery or upon evidence of book entry transfer of the collateral to the account of the custodian. To the extent that any repurchase transaction exceeds one business day, the value of the collateral is marked-to-market on a daily basis to maintain the adequacy of the collateral. If the seller defaults and the value of the collateral declines or if bankruptcy proceedings are commenced with respect to the seller of the security, realization of the collateral by the Fund may be delayed or limited. At June 30, 2017, the Fund did not hold any repurchase agreements.

Securities Sold Short. The Fund enters into short sale transactions. Short selling involves selling securities that may or may not be owned and, at times, borrowing the same securities for delivery to the purchaser, with an obligation to replace such borrowed securities at a later date. The proceeds received from short sales are recorded as liabilities and the Fund records an unrealized gain or loss to the extent of the difference between the proceeds received and the value of an open short position on the day of determination. The Fund records a realized gain or loss when the short position is closed out. By entering into a short sale, the Fund bears the market risk of an unfavorable change in the price of the security sold short. Dividends on short sales are recorded as an expense by the Fund on the ex-dividend date and interest expense is recorded on the accrual basis. The broker retains collateral for the value of the open positions, which is adjusted periodically as the value of the position fluctuates. Securities sold short and details of collateral at June 30, 2017 are reflected within the Schedule of Investments. For the six months ended June 30, 2017, the Fund incurred $19,139 in service fees related to its investment positions sold short and held by the broker. These amounts are included in the Statement of Operations under Expenses, Service fees for securities sold short.

Securities Transactions and Investment Income. Securities transactions are accounted for on the trade date with realized gain/(loss) on investments determined by using the identified cost method. Interest income (including amortization of premium and accretion of discount) is recorded on the accrual basis. Premiums and discounts on debt securities are amortized using the effective yield to maturity method. Dividend income is recorded on

10

GAMCO Mathers Fund

Notes to Financial Statements (Unaudited) (Continued)

the ex-dividend date, except for certain dividends from foreign securities that are recorded as soon after the ex-dividend date as the Fund becomes aware of such dividends.

Expenses. Certain administrative expenses are common to, and allocated among, various affiliated funds. Such allocations are made on the basis of each fund’s average net assets or other criteria directly affecting the expenses as determined by the Adviser pursuant to procedures established by the Board.

Distributions to Shareholders. Distributions to shareholders are recorded on the ex-dividend date. Distributions to shareholders are based on income and capital gains as determined in accordance with federal income tax regulations, which may differ from income and capital gains as determined under GAAP. These differences are primarily due to differing treatments of income and gains on various investment securities held by the Fund, timing differences, and differing characterizations of distributions made by the Fund. These book/ tax differences are either temporary or permanent in nature. To the extent these differences are permanent, adjustments are made to the appropriate capital accounts in the period when the differences arise. These reclassifications have no impact on the net asset value (“NAV”) per share of the Fund.

No distributions were made during the year ended December 31, 2016.

Provision for Income Taxes. The Fund intends to continue to qualify as a regulated investment company under Subchapter M of the Internal Revenue Code of 1986, as amended (the “Code”). It is the policy of the Fund to comply with the requirements of the Code applicable to regulated investment companies and to distribute substantially all of its net investment company taxable income and net capital gains. Therefore, no provision for federal income taxes is required.

At December 31, 2016, the Fund had net capital loss carryforwards for federal income tax purposes which are available to reduce future required distributions of net capital gains to shareholders. Under the Regulated Investment Company Modernization Act of 2010, the Fund is permitted to carry forward for an unlimited period capital losses incurred in years beginning after December 22, 2010. In addition, these losses must be utilized prior to the losses incurred in pre-enactment taxable years. As a result of the rule, pre-enactment capital loss carryforwards may have an increased likelihood of expiring unused. Additionally, post enactment capital losses that are carried forward will retain their character as either short term or long term capital losses rather than being considered all short term as under previous law.

Capital loss carryforward available through 2018	$	151,917
Short term capital loss carryforward with no expiration		4,524,465
Total capital loss carryforwards	$	4,676,382

The following summarizes the tax cost of investments, proceeds from short sales, and the related net unrealized depreciation at June 30, 2017:

	Cost/ (Proceeds)				Gross Unrealized Appreciation			Gross Unrealized Depreciation				Net Unrealized Appreciation /Depreciation
Investments		$	9,779,117			$	790			—			$	790
Securities sold short			(4,490,215	)			12,259		$	(400,964	)			(388,705	)
						$	13,049		$	(400,964	)		$	(387,915	)

11

GAMCO Mathers Fund

Notes to Financial Statements (Unaudited) (Continued)

The Fund is required to evaluate tax positions taken or expected to be taken in the course of preparing the Fund’s tax returns to determine whether the tax positions are “more-likely-than-not” of being sustained by the applicable tax authority. Income tax and related interest and penalties would be recognized by the Fund as tax expense in the Statement of Operations if the tax positions were deemed not to meet the more-likely-than-not threshold. For the six months ended June 30, 2017, the Fund did not incur any income tax, interest, or penalties. As of June 30, 2017, the Adviser has reviewed all open tax years and concluded that there was no impact to the Fund’s net assets or results of operations. The Fund’s federal and state tax returns for the prior three fiscal years remain open, subject to examination. On an ongoing basis, the Adviser will monitor the Fund’s tax positions to determine if adjustments to this conclusion are necessary.

3. Investment Advisory Agreement and Other Transactions. The Fund has entered into an investment advisory agreement (the “Advisory Agreement”) with the Adviser which provides that the Fund will pay the Adviser a fee, computed daily and paid monthly, at the annual rate of 1.00% of the value of its average daily net assets. In accordance with the Advisory Agreement, the Adviser provides a continuous investment program for the Fund’s portfolio, oversees the administration of all aspects of the Fund’s business and affairs, and pays the compensation of all Officers and Trustees of the Fund who are affiliated persons of the Adviser.

The Fund pays each Trustee who is not considered an affiliated person an annual retainer of $3,000 plus $1,000 for each Board meeting attended, and they are reimbursed for any out of pocket expenses incurred in attending meetings. All Board committee members receive $500 per meeting attended and the Chairman of the Audit Committee and the Lead Trustee each receive an annual fee of $1,000. A Trustee may receive a single meeting fee, allocated among the participating funds, for participation in certain meetings held on behalf of multiple funds. Trustees who are directors or employees of the Adviser or an affiliated company receive no compensation or expense reimbursement from the Fund.

4. Distribution Plan. The Fund’s Board has adopted a distribution plan (the “Plan”) pursuant to Rule 12b-1 under the 1940 Act. Under the Plan, payments are authorized to G.distributors, LLC (the “Distributor”), an affiliate of the Adviser, at an annual rate of 0.25% of its average daily net assets, the annual limitation under the Plan. Such payments are accrued daily and paid monthly.

5. Portfolio Securities. There were no purchases or sales of securities during the six months ended June 30, 2017 other than short term securities and U.S. Government obligations.

6. Line of Credit. The Fund participates in an unsecured line of credit, which expires on March 8, 2018 and may be renewed annually, of up to $75,000,000 under which it may borrow up to 10% of its net assets from the custodian for temporary borrowing purposes. Borrowings under this arrangement bear interest at a floating rate equal to the higher of the overnight Federal Funds rate plus 125 basis points or the 30 day LIBOR plus 125 basis points in effect on that day. This amount, if any, would be included in “Interest expense” in the Statement of Operations. During the six months ended June 30, 2017, there were no borrowings under the line of credit.

12

GAMCO Mathers Fund

Notes to Financial Statements (Unaudited) (Continued)

7. Shares of Beneficial Interest. Transactions in shares of beneficial interest were as follows:

	Six Months Ended June 30, 2017 (Unaudited)						Year Ended December 31, 2016
	Shares			Amount			Shares			Amount
Shares sold.		208,295		$	1,134,978			3,113,623		$	21,611,442
Shares redeemed		(538,149	)		(3,011,894	)		(3,075,578	)		(20,360,901	)
Net increase/(decrease)		(329,854	)	$	(1,876,916	)		38,045		$	1,250,541

The Fund imposes a redemption fee of 2.00% on shares that are redeemed or exchanged on or before the seventh day after the date of a purchase. The redemption fee is deducted from the proceeds otherwise payable to the redeeming shareholders and is retained by the Fund as an increase in paid-in capital. The redemption fees retained by the Fund during the six months ended June 30, 2017 and the year ended December 31, 2016, if any, can be found in the Statement of Changes in Net Assets under Redemption Fees.

8. Indemnifications. The Fund enters into contracts that contain a variety of indemnifications. The Fund’s maximum exposure under these arrangements is unknown. However, the Fund has not had prior claims or losses pursuant to these contracts. Management has reviewed the Fund’s existing contracts and expects the risk of loss to be remote.

9. Subsequent Events. Management has evaluated the impact on the Fund of all subsequent events occurring through the date the financial statements were issued and has determined that there were no subsequent events requiring recognition or disclosure in the financial statements.

13

Gabelli/GAMCO Funds and Your Personal Privacy

Who are we?

The Gabelli/GAMCO Funds are investment companies registered with the Securities and Exchange Commission under the Investment Company Act of 1940. We are managed by Gabelli Funds, LLC and GAMCO Asset Management Inc., which are affiliated with GAMCO Investors, Inc. that is a publicly held company with subsidiaries and affiliates that provide investment advisory services for a variety of clients.

What kind of non-public information do we collect about you if you become a fund shareholder?

If you apply to open an account directly with us, you will be giving us some non-public information about yourself. The non-public information we collect about you is:

● Information you give us on your application form. This could include your name, address, telephone number, social security number, bank account number, and other information.

● Information about your transactions with us, any transactions with our affiliates, and transactions with the entities we hire to provide services to you. This would include information about the shares that you buy or redeem. If we hire someone else to provide services — like a transfer agent — we will also have information about the transactions that you conduct through them.

What information do we disclose and to whom do we disclose it?

We do not disclose any non-public personal information about our customers or former customers to anyone other than our affiliates, our service providers who need to know such information, and as otherwise permitted by law. If you want to find out what the law permits, you can read the privacy rules adopted by the Securities and Exchange Commission. They are in volume 17 of the Code of Federal Regulations, Part 248. The Commission often posts information about its regulations on its website, www.sec.gov.

What do we do to protect your personal information?

We restrict access to non-public personal information about you to the people who need to know that information in order to provide services to you or the fund and to ensure that we are complying with the laws governing the securities business. We maintain physical, electronic, and procedural safeguards to keep your personal information confidential.

GAMCO MATHERS FUND

One Corporate Center

Rye, NY 10580-1422

Portfolio Manager Biography

Henry G. Van der Eb, CFA, joined Gabelli Funds, LLC in 1999 as President and Portfolio Manager of the GAMCO Mathers Fund which he has managed for over twenty years. He is also a Senior Vice President of GAMCO Investors, Inc. Prior to joining Gabelli, he was the owner and President of Mathers & Company, a Chicago based investment advisory firm, and Chairman of the Mathers Fund. He served as President of the Investment Analysts Society of Chicago from 1979 — 1980. Mr. Van der Eb received an M.B.A. with honors from Northwestern University Graduate School of Management and a B.A. from Vanderbilt University.

We have separated the portfolio manager’s commentary from the financial statements and investment portfolio due to corporate governance regulations stipulated by the Sarbanes-Oxley Act of 2002. We have done this to ensure that the content of the portfolio manager’s commentary is unrestricted. Both the commentary and the financial statements, including the portfolio of investments, will be available on our website at www.gabelli.com.

GAMCO MATHERS FUND

One Corporate Center

Rye, New York 10580-1422

t    800-GABELLI (800-422-3554)

f   914-921-5118

e  info@gabelli.com

    GABELLI.COM

Net Asset Value per share available daily

by calling 800-GABELLI after 7:00 P.M.

BOARD OF TRUSTEES

Mario J. Gabelli, CFA

Chairman and Chief

Executive Officer,

GAMCO Investors, Inc.

Executive Chairman,

Associated Capital Group, Inc.

M. Bruce Adelberg

Consultant,

MBA Research Group

E. Val Cerutti

Chief Executive Officer,

Cerutti Consultants, Inc.

Anthony S. Colavita

Attorney,

Anthony S. Colavita, P.C.

Vincent D. Enright

Former Senior Vice President

and Chief Financial Officer,

KeySpan Corp.

Anthony R. Pustorino

Certified Public Accountant,

Professor Emeritus,

Pace University

Werner J. Roeder, MD

Former Medical Director,

Lawrence Hospital

Henry G. Van der Eb, CFA

President and Chief Executive

Officer,

GAMCO Mathers Fund

Anthonie C. van Ekris

Chairman,

BALMAC International, Inc.

OFFICERS

Bruce N. Alpert

Executive Vice President

Agnes Mullady

Vice President

Andrea R. Mango

Secretary

John C. Ball

Treasurer

Richard J. Walz

Chief Compliance Officer

Anne E. Morrissy, CFA

Executive Vice President

Heidi M. Koontz

Vice President

Edith L. Cook

Vice President

DISTRIBUTOR

G.distributors, LLC

CUSTODIAN, TRANSFER

AGENT, AND DIVIDEND

DISBURSING AGENT

State Street Bank and Trust

Company

LEGAL COUNSEL

Paul Hastings LLP

This report is submitted for the general information of the shareholders of the GAMCO Mathers Fund. It is not authorized for distribution to prospective investors unless preceded or accompanied by an effective prospectus.

GAB1726Q217SR

Item 2. Code of Ethics.

Not applicable.

Item 3. Audit Committee Financial Expert.

Not applicable.

Item 4. Principal Accountant Fees and Services.

Not applicable.

Item 5. Audit Committee of Listed Registrants.

Not applicable.

Item 6. Investments.

(a) Schedule of Investments in securities of unaffiliated issuers as of the close of the reporting period is included as part of the report to shareholders filed under Item 1 of this form.

(b) Not applicable.

Item 7. Disclosure of Proxy Voting Policies and Procedures for Closed-End Management Investment Companies.

Not applicable.

Item 8. Portfolio Managers of Closed-End Management Investment Companies.

Not applicable.

Item 9. Purchases of Equity Securities by Closed-End Management Investment Company and Affiliated Purchasers.

Not applicable.

Item 10. Submission of Matters to a Vote of Security Holders.

There have been no material changes to the procedures by which the shareholders may recommend nominees to the registrant’s Board of Trustees, where those changes were implemented after the registrant last provided disclosure in response to the requirements of Item 407(c)(2)(iv) of Regulation S-K (17 CFR 229.407) (as required by Item 22(b)(15) of Schedule 14A (17 CFR 240.14a-101)), or this Item.

Item 11. Controls and Procedures.

(a) The registrant’s principal executive and principal financial officers, or persons performing similar functions, have concluded that the registrant’s disclosure controls and procedures (as defined in Rule 30a-3(c) under the Investment Company Act of 1940, as amended (the “1940 Act”) (17 CFR 270.30a-3(c))) are effective, as of a date within 90 days of the filing date of the report that includes the disclosure required by this paragraph, based on their evaluation of these controls and procedures required by Rule 30a-3(b) under the 1940 Act (17 CFR 270.30a-3(b)) and Rules 13a-15(b) or 15d-15(b) under the Securities Exchange Act of 1934, as amended (17 CFR 240.13a-15(b) or 240.15d-15(b)).

(b) There were no changes in the registrant’s internal control over financial reporting (as defined in Rule 30a-3(d) under the 1940 Act (17 CFR 270.30a-3(d))) that occurred during the registrant’s second fiscal quarter of the period covered by this report that has materially affected, or is reasonably likely to materially affect, the registrant’s internal control over financial reporting.

Item 12. Exhibits.

(a)(1) Not applicable.

(a)(2) Certifications pursuant to Rule 30a-2(a) under the 1940 Act and Section 302 of the Sarbanes-Oxley Act of 2002 are attached hereto.

(a)(3) Not applicable.

(b) Certifications pursuant to Rule 30a-2(b) under the 1940 Act and Section 906 of the Sarbanes-Oxley Act of 2002 are attached hereto.

SIGNATURES

Pursuant to the requirements of the Securities Exchange Act of 1934 and the Investment Company Act of 1940, the registrant has duly caused this report to be signed on its behalf by the undersigned, thereunto duly authorized.

(Registrant)      The GAMCO Mathers Fund                                                                          

By (Signature and Title)*    /s/ Henry G. Van der Eb                                                            

 Henry G. Van der Eb, Chief Executive Officer

Date      8/24/2017                                                                                                                   

Pursuant to the requirements of the Securities Exchange Act of 1934 and the Investment Company Act of 1940, this report has been signed below by the following persons on behalf of the registrant and in the capacities and on the dates indicated.

By (Signature and Title)*    /s/ Henry G. Van der Eb                                                            

 Henry G. Van der Eb, Chief Executive Officer

Date      8/24/2017                                                                                                                   

By (Signature and Title)*    /s/ John C. Ball                                                                          

 John C. Ball, Principal Financial Officer and Treasurer

Date      8/24/2017                                                                                                                   

^* Print the name and title of each signing officer under his or her signature.