Opinion Letter – In-House Counsel – Debt Securities Under Indenture – UnitedHealth Group Inc.

9900 Bren Road East

Minnetonka, Minnesota 55343

March 8, 2012

Board of Directors

UnitedHealth Group Incorporated

300 UnitedHealth Group Center

9900 Bren Road East

Minnetonka, Minnesota 55343

Ladies and Gentlemen:

I have acted as Senior Deputy General Counsel to UnitedHealth Group
Incorporated, a Minnesota corporation (the
“Company“), in connection with the Underwriting
Agreement, dated March 5, 2012 (the “Underwriting
Agreement“), among the Company and Merrill Lynch, Pierce, Fenner
& Smith Incorporated, Barclays Capital Inc., Citigroup Global Markets Inc.
and Credit Suisse Securities (USA) LLC, as representatives (the
“Representatives“) of the several underwriters named
in the Pricing Agreement, dated March 5, 2012 (“Pricing
Agreement“), among the Company and the Representatives, and the
Pricing Agreement relating to the proposed issuance by the Company of its 2.875%
Notes due March 15, 2022 in the aggregate principal amount of $600,000,000 (the
“2022 Notes“) and its 4.375% Notes due March 15, 2042
in the aggregate principal amount of $400,000,000 (the “2042
Notes” and collectively with the 2022 Notes, the
“Debt Securities“). The Debt Securities are issuable
under the Indenture, dated as of February 4, 2008 (the
“Indenture“), between the Company and U.S. Bank
National Association, as trustee, as supplemented by that certain Officers153
Certificate and Company Order dated March 8, 2012, relating to the 2022 Notes
and that certain Officers153 Certificate and Company Order dated March 8, 2012,
relating to the 2042 Notes. This opinion letter is furnished to you at your
request to enable you to fulfill the requirements of Item 601(b)(5) of
Regulation S-K, 17 C.F.R. § 229.601(b)(5), in connection with the Registration
Statement. Capitalized terms used herein and not otherwise defined herein shall
have the meanings assigned to them in the Underwriting Agreement or the Pricing
Agreement, as applicable.

For purposes of this opinion letter, I, or attorneys in the legal department
of the Company under my direction, have examined copies of such documents and
reviewed such questions of law as I have considered necessary and appropriate
for the purposes of this opinion.

In rendering the opinions set forth below, I have assumed the genuineness of
all signatures, the accuracy and completeness of all documents submitted to me,
the authenticity of all original documents, and the conformity to authentic
original documents of all documents submitted to me

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Board of Directors

UnitedHealth Group Incorporated

Page 2

as copies (including telecopies). I have also assumed the legal capacity for
all purposes relevant hereto of all natural persons and, with respect to all
parties to agreements or instruments relevant hereto other than the Company,
that such parties had the requisite power and authority (corporate or otherwise)
to execute, deliver and perform such agreements or instruments, that such
agreements or instruments have been duly authorized by all requisite action
(corporate or otherwise), executed and delivered by such parties and that such
agreements or instruments are the valid, binding and enforceable obligations of
all parties thereto. As to questions of fact material to my opinion, I have
relied upon certificates of officers of the Company and of public officials. I
have also assumed that any Debt Securities will be issued and sold with such
terms and in such manner as are described in the Registration Statement (as
amended from time to time), the Prospectus included therein (as amended from
time to time) and any related supplements to the Prospectus. This opinion letter
is given, and all statements herein are made, in the context of the foregoing.

Based upon, subject to and limited by the foregoing, I am of the opinion
that:

(i)

The Company has the corporate power to issue the Debt Securities and the Company has taken all necessary corporate action with respect to such issuance.

(ii)

The Indenture has been duly authorized, executed and delivered by the Company.

This opinion letter has been prepared for your use in connection with the
Registration Statement and speaks as of the date hereof. I assume no obligation
to advise you of any changes in the foregoing subsequent to the effective date
of the Registration Statement.

The opinions expressed above are limited to the laws of the State of
Minnesota.

I hereby consent to the filing of this opinion letter as Exhibit 5.1 to a
Current Report on Form 8-K of the Company filed with the Securities and Exchange
Commission and thereby incorporated by reference into that Registration
Statement and to the reference to this opinion under the caption “Legal Matters”
in the prospectus constituting a part of the Registration Statement. In giving
this consent, I do not hereby admit that I am an “expert” within the meaning of
the Securities Act of 1933, as amended. Hogan Lovells US LLP may rely on the
opinions expressed in paragraphs (i) and (ii), insofar as they relate to
Minnesota law, for purposes of delivering their legal opinion in connection with
the validity of the Debt Securities.

Very truly yours,

/s/ Kuai H. Leong

Kuai H. Leong

Senior Deputy General Counsel