<Page>
UNITED STATES
SECURITIES AND EXCHANGE COMMISSION
WASHINGTON, D.C. 20549
------------------
FORM 11-K
(Mark One):
/X/ ANNUAL REPORT PURSUANT TO SECTION 15(d) OF THE SECURITIES EXCHANGE ACT
OF 1934
For the fiscal year ended December 31, 2002
OR
/ / TRANSITION REPORT PURSUANT TO SECTION 15(d) OF THE SECURITIES EXCHANGE
ACT OF 1934
For the transition period from ______________ to ___________
Commission file number: 1-13503
A. Full title of the plan and address of the plan, if different from that
of the issuer named below:
SI BANK & TRUST 401(k) SAVINGS PLAN IN RSI RETIREMENT TRUST
B. Name of issuer of the securities held pursuant to the plan and the
address of its principal executive office:
STATEN ISLAND BANCORP, INC.
1535 RICHMOND AVENUE
STATEN ISLAND, NEW YORK 10314
<Page>
REQUIRED INFORMATION
FINANCIAL STATEMENTS. The following financial statements and schedule
are filed as part of this annual report for the SI Bank & Trust 401(k) Savings
Plan in RSI Retirement Trust (the "Plan"):
<Table>
<Caption>
Page No.
-------
Report of Independent Accountants .................................................. 1
Financial Statements
Statement of Net Assets Available for Benefits as of
December 31, 2002 and 2001 .................................................2
Statement of Changes in Net Assets Available for Benefits
for the Year Ended December 31, 2002....................................... 3
Notes to Financial Statements........................................................4-8
Supplemental Schedule*
Schedule H, Line 4i-Schedule of Assets (Held at End of Year).....................9
</Table>
* Other schedules required by 29 CFR 2520.103-10 of the Department of Labor's
Rules and Regulations for Reporting and Disclosure under the Employee Retirement
Income Security Act of 1974 ("ERISA") have been omitted because they are not
applicable.
<Page>
REPORT OF INDEPENDENT ACCOUNTANTS
To the Participants and Administrator of
SI Bank 401(k) Savings Plan
In our opinion, the accompanying statements of net asset available for benefits
and the related statement of changes in net assets available for benefits
present fairly, in all material respects, the financial status of the SI Bank &
Trust 401(k) Savings Plan (the "Plan") at December 31, 2002 and 2001, and the
changes in its financial status for the year ended December 31, 2002 in
conformity with accounting principles generally accepted in the United States of
America. These financial statements are the responsibility of the Plan's
management; our responsibility is to express an opinion on these financial
statements based on our audit. We conducted our audits of these statements in
accordance with auditing standards generally accepted in the United States of
America, which require that we plan and perform the audit to obtain reasonable
assurance about whether the financial statements are free of material
misstatement. An audit includes examining on a test basis, evidence supporting
the amounts and disclosures in the financial statements, assessing the
accounting principles used and significant estimates made by management, and
evaluating the overall financial statement presentation. We believe that our
audits provide a reasonable basis for our opinion.
Our audits were conducted for the purpose of forming an opinion on the basic
financial statements taken as a whole. The supplemental Schedule of Assets (Held
at End of Year) is presented for the purpose of additional analysis and is not a
required part of the basic financial statements but is supplementary information
required by the Department of Labor's Rules and Regulations for Reporting and
Disclosure under the Employee Retirement Income Security Act of 1974. This
supplemental schedule is the responsibility of the Plan's management. The
supplemental schedule has been subjected to the auditing procedures applied in
the audit of the basic financial statements and, in our opinion, is fairly
stated in all material respects in relation to the basic financial statements
taken as whole.
/s/ PricewaterhouseCoopers LLP
June 16, 2003
1
<Page>
SI BANK & TRUST 401(k) SAVINGS PLAN 2
STATEMENTS OF NET ASSETS AVAILABLE FOR BENEFITS
- --------------------------------------------------------------------------------
<Table>
<Caption>
DECEMBER 31,
2002 2001
ASSETS
Investments stated at fair value $32,918,413 $30,425,364
Employee contribution receivable 47,462 36,199
Accrued interest receivable 3,008 4,147
----------- -----------
TOTAL ASSETS 32,968,883 30,465,710
=========== ===========
Liabilities $ - $ -
----------- -----------
NET ASSETS AVAILABLE FOR BENEFITS $32,968,883 $30,465,710
=========== ===========
</Table>
The accompanying notes are an integral part of these financial statements.
<Page>
SI BANK & TRUST 401(k) SAVINGS PLAN 3
STATEMENT OF CHANGES IN NET ASSETS AVAILABLE FOR BENEFITS
- --------------------------------------------------------------------------------
<Table>
<Caption>
FOR THE YEAR ENDED
DECEMBER 31, 2002
Additions to net assets attributed to:
Employee contributions $1,294,508
Other additions
Net appreciation in fair value of investments 2,246,826
Interest 78,078
Dividends 538,574
-----------
TOTAL ADDITIONS 4,157,986
-----------
Deductions:
Distributions to participants or beneficiaries 1,654,813
-----------
TOTAL DEDUCTIONS 1,654,813
-----------
NET INCREASE 2,503,173
-----------
Net assets available for plan benefits, beginning of year 30,465,710
-----------
Net assets available for plan benefits, end of year $32,968,883
===========
</Table>
The accompanying notes are an integral part of these financial statements.
<Page>
SI BANK & TRUST 401(k) SAVINGS PLAN 4
NOTES TO FINANCIAL STATEMENTS
- --------------------------------------------------------------------------------
1. DESCRIPTION OF THE PLAN
The following description of the SI Bank & Trust 401(k) Savings Plan (the
"Plan") provides only general information. Participants should refer to the
Plan agreement for a more complete description of the Plan's provisions.
GENERAL
The Plan is a defined contribution plan, sponsored by SI Bank & Trust (the
"Bank"), covering all salaried employees of the Bank who have completed one
year of service. It is subject to the provisions of the Employee Retirement
Income Security Act of 1974. The Bank is a wholly-owned subsidiary of
Staten Island Bancorp, Inc.
CONTRIBUTIONS
Participants may contribute a minimum of 1% up to a maximum of 25% and 8%
in 2002 and 2001, respectively, of their annual wages before bonuses and
overtime not to exceed the maximum amount permitted under the Internal
Revenue Code ($11,000 plus a catch-up contribution of $1,000 for
participants 50 years of age and older in 2002 and $10,500 in 2001). The
Bank will match 50% to 100% of participant contributions, based on years of
service up to a maximum of 6% of annual wages. Effective with a Plan
amendment during 1997, these matching contributions are made in stock to
the Staten Island Bancorp, Inc. Employee Stock Ownership Plan.
PARTICIPANT ACCOUNTS
Each participant's account is credited with the participant's contributions
and an allocation of the Bank's contribution and Plan earnings. Allocations
are based on participant earnings or account balances, as defined. The
payment to which a participant is entitled is the benefit that can be
provided from the participant's account.
DISTRIBUTIONS
Upon disability, death, retirement or termination, a participant (or
beneficiary) is entitled to receive a lump-sum distribution equal to the
value of his or her account, or installments over a period not to exceed 15
years of accumulated plan benefits. Participants may also, in certain
instances, make cash withdrawals to meet an unusual or financial emergency.
PARTICIPANT LOANS
Participants are permitted to obtain loans from the Plan in an amount of up
to 50% of the net value of their 100% vested balance, not to exceed
$50,000. Interest is charged on these loans at a rate similar to that which
would be charged at other financial institutions. Loans bear interest at a
rate between 5.25% and 10.5% for 2002 and 2001. Loan terms cannot exceed
five years unless the proceeds are used to finance the purchase of a
primary residence, in which case the term of the loan cannot exceed a
period of 15 years.
FORFEITURES
Effective January 23, 2002, all Plan forfeitures will be applied to the
Plan's administrative expense. The Plan's 2002 forfeitures of $262 included
in the Plan's net assets will be applied to administrative expenses in
2003.
Prior to January 23, 2002, forfeitures were allocated to Plan participants
once a year on a pro rata basis. The Plan's 2001 forfeitures of $6,211
included in the Plan's net assets were allocated to Plan participants in
2002.
<Page>
SI BANK & TRUST 401(k) SAVINGS PLAN 5
NOTES TO FINANCIAL STATEMENTS
- --------------------------------------------------------------------------------
VESTING
Participants are immediately vested in their voluntary contributions plus
actual earnings thereon. Prior to January 23, 2002, vesting in the
remainder of their accounts was based on years of continuous service. A
participant began to vest in the Plan according to the following Table:
<Table>
<Caption>
VESTING
YEARS OF CREDIT SERVICE PERCENTAGE
Less than 2 years 0%
2 20%
3 40%
4 60%
5 80%
6 or more 100%
</Table>
Effective January 23, 2002, participants were fully vested in all amounts
credited to their accounts under the Plan on that date.
PLAN AMENDMENTS
Effective January 23, 2002, participants entitled to an allocated dividend
may elect to have the dividend amount distributed in cash in lieu of being
reinvested in the Employer Stock Fund. As a result of the change to the
Plan, all participants were fully vested in all amounts credited to their
accounts under the Plan as of that date.
2. SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES
BASIS OF PRESENTATION
The accompanying financial statements have been prepared using the accrual
basis of accounting.
USE OF ESTIMATES
The preparation of financial statements in conformity with generally
accepted accounting principles requires the Plan administrator to make
estimates and assumptions that affect the reported amounts of additions and
deductions to net assets during the reporting period. Actual results could
differ from those estimates.
INVESTMENT VALUATION AND INCOME RECOGNITION
The trust established under the Plan is administered through participation
in the RSI Retirement Trust (the "RSI Trust"). The RSI Trust is a
tax-exempt trust registered as an open-end management investment company
under the Investment Company Act and is the Trustee of the Plan. Plan
assets held by the RSI Trust are represented as units of beneficial
interest in one or more of the investment funds offered by the RSI Trust.
The net asset value of the units of beneficial interest in each investment
fund is based on the market value of the underlying assets of the funds,
determined generally by reference to available market prices.
Net investment income and net appreciation (depreciation) in fair value of
units held represent the Plan's proportionate share of the net investment
income and realized and unrealized investment gains and losses of the RSI
Trust investment funds. Purchases and sales of securities are recorded on a
trade-date basis. Dividends are recorded on the ex-dividend date.
<Page>
SI BANK & TRUST 401(k) SAVINGS PLAN 6
NOTES TO FINANCIAL STATEMENTS
- --------------------------------------------------------------------------------
RISK AND UNCERTAINTIES
The Plan provides for various investment options in any combination of
stocks, mutual funds and other investment securities. Investment securities
are exposed to various risks, such as interest rate, market and credit
risk. Due to the level of risk associated with certain investments, it is
at least reasonably possible that changes in value of investment securities
will occur in the near term and that such changes could materially affect
participant's account balances and the amounts reported in the Statements
of Net Assets Available for Benefits and the Statement of Changes in Net
Assets Available for Benefits.
PAYMENT OF BENEFITS
Benefits are recorded when paid.
ADMINISTRATIVE COST
The Plan incurs certain administrative costs in connection with its
investment activities which are borne by the Bank.
3. INVESTMENTS
As of December 31, 2002 and 2001 the Plan assets were primarily invested in
the following funds administered by the Trustee as follows:
CORE EQUITY FUND - Consists of investments in a broadly diversified group
of large, financially sound, high-quality companies.
EMERGING GROWTH EQUITY FUND - Consists of investments primarily in smaller
companies with higher than average returns on equity, earnings growth
potential and dividend growth potential. The fund's holdings focus on
companies with market capitalization of less than $1 billion.
VALUE EQUITY FUND - Consists of investments in financially sound companies
that have low price earnings ratios, above average dividend yields,
favorable price-to-book ratios, and are currently out of favor in the
marketplace.
ACTIVELY MANAGED BOND - Consists of investments in high quality bonds with
a full spectrum of maturities (0-30 years).
INTERMEDIATE-TERM BOND FUND - Consists of investments in high-quality fixed
income securities that mature within ten years or have an expected average
life of ten years or less. In terms of quality, at all times at least 50%
of the investments must be in U.S. Government issues and at least 75% of
the total investments must be instruments rated "AA" or better by certain
rating agencies.
SHORT-TERM INVESTMENT FUND - Consists of investments in high-quality cash
equivalent type investments offering substantial liquidity and capital
preservation. The average maturity of the fund's holdings is less than one
year.
INTERNATIONAL EQUITY FUND - Consists of investments in stocks that are
headquartered in foreign countries.
EMPLOYER STOCK FUND - Consists of investments in the common stock of Staten
Island Bancorp, Inc. and other short-term high-quality cash equivalent type
investments.
<Page>
SI BANK & TRUST 401(k) SAVINGS PLAN 7
NOTES TO FINANCIAL STATEMENTS
- --------------------------------------------------------------------------------
FORFEITURE FUND - Consists of forfeitures which will be reallocated to plan
participants or applied to administrative expenses at a later date.
INVESTMENTS HELD
Investments held by the Plan are summarized below. Those investments that
represent 5 percent or more of the Plan's net assets at the end of the year
are noted with an asterisk (*). Those investments that are
nonparticipant-directed are noted with two asterisks (**). Those
investments that include participant and nonparticipant-directed
investments are noted with a plus sign (+).
<Table>
<Caption>
DECEMBER 31, 2002 DECEMBER 31, 2001
SHARES/UNITS FAIR VALUE SHARES/UNITS FAIR VALUE
RS Group Federated Prime
Obligation Fund** 64,779 $ 64,779 - $ -
RS Group Cash Forfeiture Fund** 262 262 6,211 6,211
RSI Retirement Trust Core
Equity Fund 52,624 3,289,006* 57,853 5,142,575 *
RSI Retirement Trust Emerging
Growth Equity Fund 14,783 750,699 14,182 1,262,727
RSI Retirement Trust Value
Equity Fund 15,212 1,041,533 13,707 1,157,018
RSI Retirement Trust
International Equity Fund 988 39,496 505 24,799
RSI Retirement Trust
Intermediate Term Bond Fund 20,224 858,303 10,527 427,810
RSI Retirement Trust Actively
Managed Bond Fund 26,379 1,302,890 13,556 615,828
RSI Retirement Trust
Short-term Bond Fund 42,335 1,119,334 43,566 1,133,152
----------- -----------
TOTAL 8,466,302 9,770,120
----------- -----------
SI Bancorp
Common Stock Fund + 1,271,109 $23,390,384 * 1,693,360 $19,664,634 *
Participant loans 1,061,727 990,610
----------- -----------
TOTAL $32,918,413 $30,425,364
=========== ===========
</Table>
4. PLAN TERMINATION
The Bank intends to continue the Plan indefinitely but reserves the right
to amend or terminate it. If the Plan is terminated or if there is a
complete discontinuance of contributions, the Plan participants will be
fully vested in their rights under the Plan.
<Page>
SI BANK & TRUST 401(k) SAVINGS PLAN 8
NOTES TO FINANCIAL STATEMENTS
- --------------------------------------------------------------------------------
5. TAX STATUS
The Plan obtained its latest determination letter on March 26, 2003 in
which the Internal Revenue Service stated that the Plan was in compliance
with the applicable requirements of the Internal Revenue Code.
6. RELATED PARTY TRANSACTIONS
One of the investment funds of the Plan invests in shares of Staten Island
Bancorp, Inc. The Plan owned 1,155,657 shares of common stock in the
Employer Stock Fund as of December 31, 2002 with a market value of
$23,274,932. As of December 31, 2001, the Plan owned 1,173,887 shares of
common stock with a market value of $19,146,102.
<Page>
SI BANK & TRUST 401(k) SAVINGS PLAN 9
SCHEDULE H, LINE 4i - SCHEDULE OF ASSETS (HELD AT END OF YEAR)
- --------------------------------------------------------------------------------
<Table>
<Caption>
(c) Description of
investment including
(b) Identity of issue, maturity date rate
borrower, lessor, or of interest, collateral (e) Current
(a) similar party par, or maturity value (d) Cost value
- ---- ------------------------------- ---------------------- ---------- ------------
* RSI Retirement Core Equity Fund 52,624 shares $2,805,165 $3,289,006
RSI Retirement Emerging Growth
* Equity Fund 14,783 shares 1,084,461 750,699
* RSI Retirement Value Equity Fund 15,212 shares 1,162,557 1,041,533
* RSI Retirement International
Equity Fund 988 shares 47,211 39,496
* RSI Retirement Intermediate-Term
Bond Fund 20,224 shares 842,882 858,303
RSI Retirement Actively Managed
* Bond Fund 26,379 shares 1,216,108 1,302,890
RSI Retirement Short-Term
* Investment Fund 42,335 shares 1,106,593 1,119,334
* SI Bancorp employer stock
fund 1,271,109 shares 8,744,707 23,390,384
* RS Group Forfeiture Fund 262 shares 262 262
* RS Group Federated Prime
Obligation Fund 64,779 shares 64,779 64,779
Participant loans Interest rate - 1,061,727
5.25% - 10.5% ----------- -----------
TOTAL ASSETS HELD FOR
INVESTMENT PURPOSES $17,074,725 $32,918,413
=========== ===========
</Table>
*Parties-in-interest to the Plan.
<Page>
SIGNATURES
THE PLAN. Pursuant to the requirements of the Securities Exchange Act
of 1934, the trustees for the Plan have duly caused this annual report to be
signed by the undersigned hereunto duly authorized.
SI BANK & TRUST 401(k) SAVINGS PLAN
IN RSI RETIREMENT TRUST
June 25, 2003 By: /s/ Catherine Arcuri
--------------------
Name: Catherine Arcuri
Title: Plan Administrator
<Page>
INDEX TO EXHIBITS
<Table>
<Caption>
Number Description
------ -----------
23 Consent of Independent Accountants
99 Statement Pursuant to 18 U.S.C. Section 1350 as Required by
Section 906 of the Sarbanes-Oxley Act of 2002
</Table>