Report of Independent Registered Public Accounting Firm

To the Shareholders of MFS Global Opportunistic Bond Fund and
Board of Trustees of MFS Series Trust X

In planning and performing our audit of the financial statements of MFS
Global Opportunistic Bond Fund (the "Fund") (one of the portfolios
comprising the MFS Series Trust X (the "Trust")) as of and for the year
ended November 30, 2022, in accordance with the standards of the
Public Company Accounting Oversight Board (United States) (PCAOB),
we considered the Trust's 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 the Trust's internal control over financial reporting.
Accordingly, we express no such opinion.

The management of the Trust 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 company'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 company'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 company; (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
company are being made only in accordance with authorizations of
management and directors of the company; and (3) provide reasonable
assurance regarding prevention or timely detection of unauthorized
acquisition, use or disposition of a company'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 company's annual or
interim financial statements will not be prevented or detected on a
timely basis.

Our consideration of the Trust's 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 PCAOB.
However, we noted no deficiencies in the Trust's 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 November 30, 2022.

This report is intended solely for the information and use of
management and the Board of Trustees of MFS Series Trust X and the
Securities and Exchange Commission and is not intended to be and
should not be used by anyone other than these specified parties.


/s/ Ernst & Young LLP
Boston, Massachusetts
January 13, 2023