Report of Independent Registered Public Accounting
Firm To the Shareholders and
Board of Trustees of William Blair Funds

In planning and performing our audit of the financial
statements of William Blair Growth Fund, William
Blair Large Cap Growth Fund, William Blair Mid Cap
Growth Fund, William Blair Small-Mid Cap Growth
Fund, William Blair Small-Mid Cap Value Fund,
William Blair Small Cap Growth Fund, William Blair
Small Cap Value Fund, William Blair Global Leaders
Fund, William Blair International Leaders Fund,
William Blair International Developed Plus Fund,
William Blair International Growth Fund, William
Blair Institutional Developed Plus Fund, William
Blair International Growth Fund, William Blair
Institutional International Growth Fund, William Blair
International Small Cap Growth Fund, William Blair
Emerging Markets Leaders Fund, William Blair
Emerging Markets Growth Fund, William Blair
Emerging Small Cap Growth Fund, William Blair
Bond Fund, William Blair Income Fund, William
Blair Low Duration Fund, and William Blair Macro
Allocation Fund as of and for the year ended
December 31, 2018, in accordance with the standards
of the Public Company Accounting Oversight Board
(United States), we considered William Blair Funds'
internal control over financial reporting, including
controls over safeguarding securities, as a basis for
designing our auditing procedures for the purpose of
expressing our opinion on the financial statements and
to comply with the requirements of Form N-CEN, but
not for the purpose of expressing an opinion on the
effectiveness of William Blair Funds' internal control
over financial reporting. Accordingly, we express no
such opinion.

The management of the William Blair Funds is
responsible for establishing and maintaining effective
internal control over financial reporting. In fulfilling
this responsibility, estimates and judgments by
management are required to assess the expected
benefits and related costs of controls. A fund's
internal control over financial reporting is a process
designed to provide reasonable assurance regarding
the reliability of financial reporting and the
preparation of financial statements for external
purposes in accordance with U.S. generally accepted
accounting principles. A fund's internal control over
financial reporting includes those policies and
procedures that (1) pertain to the maintenance of
records that, in reasonable detail, accurately and fairly
reflect the transactions and dispositions of the assets
of the funds; (2) provide reasonable assurance that
transactions are recorded as necessary to permit
preparation of financial statements in accordance with
U.S. generally accepted accounting principles, and
that receipts and expenditures of the fund are being
made only in accordance with authorizations of
management and directors of the funds; and (3)
provide reasonable assurance regarding
prevention or timely detection of unauthorized
acquisition, use or disposition of a fund's assets that
could have a material effect on the financial
statements.

Because of its inherent limitations, internal control
over financial reporting may not prevent or detect
misstatements. Also, projections of any evaluation of
effectiveness to future periods are subject to the risk
that controls may become inadequate because of
changes in conditions, or that the degree of
compliance with the policies or procedures may
deteriorate.

A deficiency in internal control over financial
reporting exists when the design or operation of a
control does not allow management or employees, in
the normal course of performing their assigned
functions, to prevent or detect misstatements on a
timely basis. A material weakness is a deficiency, or a
combination of deficiencies, in internal control over
financial reporting, such that there is a reasonable
possibility that a material misstatement of the fund's
annual or interim financial statements will not be
prevented or detected on a timely basis.

Our consideration of the William Blair Funds' internal
control over financial reporting was for the limited
purpose described in the first paragraph and would not
necessarily disclose all deficiencies in internal control
that might be material weaknesses under standards
established by the Public Company Accounting
Oversight Board (United States). However, we noted
no deficiencies in the William Blair Funds' internal
control over financial reporting and its operation,
including controls over safeguarding securities, that
we consider to be a material weakness as defined
above as of December 31, 2018.

This report is intended solely for the information and
use of management and the Board of Directors of
William Blair Funds and the Securities and Exchange
Commission and is not intended to be and should not
be used by anyone other than these specified parties.

Ernst & Young LLP

Chicago, Illinois
February 27, 2019