<PAGE>   1
                                [LIFEMARK LOGO]

                                                                      EXHIBIT 99


FOR FURTHER INFORMATION PLEASE CONTACT:

Michael J. Kennedy                                Bob Hussey
Lifemark Corporation                              EverCare
(602) 331-5150                                    (952) 936-3629
e-mail:  investors@lifemarkcorp.com               e-mail: rhusse@uhc.com

                   LIFEMARK CORPORATION TO MERGE WITH EVERCARE
              Merger Will Create National Organization Serving the
      Health and Well-Being Needs of America's Elderly Across Care Settings

PHOENIX, AZ, October 10, 2000--Lifemark Corporation (Nasdaq: LMRK) today
announced that it will merge with EverCare, an operating unit of Ovations, which
is a subsidiary of UnitedHealth Group (NYSE: UNH). The merger will create a
national leader in serving the health and well-being needs of America's elderly
across the full continuum of care settings.

Rhonda Brede, chief executive officer of Lifemark, stated "This merger is a
wonderful opportunity to integrate two of the leading organizations in the
country serving frail, vulnerable and elderly people. Together, we will
establish ourselves as the preeminent providers of health and well-being
services for these individuals."

Marcia Smith, chief executive officer of EverCare, commented that "While we both
seek to help the elderly live better lives, we currently operate in different
markets serving different groups of people. Combining our resources creates a
powerful platform that allows us to expand our ability to deliver better care to
more people."

The combined company will operate as EverCare, with Ms. Smith as the chief
executive officer and Ms. Brede as chief operating officer. It will conduct
business in over a dozen states, serving Medicare, Medicaid, and private-pay
patients in a variety of care settings, including home, community-based and
nursing facilities.

Lifemark shareholders will be entitled to receive shares of UnitedHealth Group
Common Stock having a value of $63 million or $10.55 per Lifemark share on a
fully diluted basis, so long as the average ten-day closing price of
UnitedHealth Group stock immediately preceding the transaction close remains at
or between $95.00 and $113.00 per share. In the event the average ten-day
closing price of UnitedHealth Group stock immediately preceding the transaction
close is above $113 per share, Lifemark shareholders will receive a total of
557,500 UnitedHealth Group shares and the merger consideration may thereby
increase based on UnitedHealth Group's stock appreciation above $113.00. If the
average ten-day closing price of UnitedHealth Group stock immediately preceding
the transaction is at or between $88.00 and $95.00 per share, the value Lifemark
shareholders will receive will decrease proportionately from $63 million or
$10.55 per share to $60
<PAGE>   2
million or $10.08 per share. If the average ten-day closing price of
UnitedHealth Group Common Stock preceding the transaction close is below $88.00
per share, UnitedHealth Group has the option to pay $10.08 per share of merger
consideration in either cash or shares of UnitedHealth Group Common Stock.

The transaction is subject to approval by Lifemark's shareholders. Shareholders
of Lifemark holding approximately 40% of the outstanding shares of Lifemark
common stock have entered into a voting agreement with UnitedHealth Group
whereby they have agreed to vote their shares in favor of the merger. The merger
is also subject to approvals by certain antitrust and state regulators. Lifemark
and UnitedHealth Group anticipate closing the transaction near the end of the
year.

ABOUT LIFEMARK

Lifemark develops, coordinates, and administers all aspects of specialty,
risk-based care management programs designed to improve the quality of life for
vulnerable, frail elderly and chronically ill patients. Lifemark manages both
the financing and delivery of comprehensive health care services that create
fundamental change in the well-being of its customers. In fiscal year 2000
(ended 5/31/00), Lifemark had revenues of approximately $150 million,
representing a 75% increase over 1999. Lifemark is based in Phoenix, Arizona and
has regional offices in Arkansas, California, Hawaii, Indiana, Michigan, New
Mexico and Texas.

ABOUT EVERCARE

Founded in 1987, EverCare has pioneered coordinated care for frail elderly
persons in nursing homes. EverCare provides direct medical care through nurse
practitioner/physician primary care teams and seeks to provide as much care
"on-site" in the nursing home as possible. EverCare also helps ensure close
communication among families, physicians and nursing home staff regarding a
resident's care. EverCare serves 18,000 patients in over 450 nursing homes.

EverCare is headquartered in Minnetonka, Minnesota and conducts business in
Arizona, Colorado, Florida, Georgia, Illinois, Maryland, Massachusetts, New York
and Ohio. EverCare is part of Ovations, a subsidiary of UnitedHealth Group.

FORWARD LOOKING STATEMENTS

Statements that EverCare, Lifemark, or UnitedHealth Group may publish, including
those in this announcement, that are not strictly historical are
"forward-looking" statements under the safe harbor provisions of the Private
Securities Litigation Reform Act of 1995. Forward-looking statements involve
known and unknown risks, which may cause actual results and corporate
developments to differ materially from those expected. Factors that could cause
results and developments to differ materially from expectations include, without
limitation, the failure of the Lifemark shareholders to approve the merger; the
risk that the businesses of Lifemark and EverCare will not be integrated
successfully; disruptions from the merger making it more difficult to maintain
relationships with
<PAGE>   3
clients, employees and other third parties; and the effects of state and federal
regulations. Additional factors that could cause UnitedHealth Group's and
Lifemark's results to differ materially from those described in the
forward-looking statements can be found in each of UnitedHealth Group's and
Lifemark's respective SEC reports, including quarterly reports on Form 10-Q,
annual reports on Form 10-K, and reports on Form 8-K.

OTHER IMPORTANT INFORMATION

IN CONNECTION WITH THE TRANSACTION DESCRIBED IN THIS ANNOUNCEMENT, UNITEDHEALTH
GROUP WILL FILE A REGISTRATION STATEMENT ON FORM S-4 AND OTHER RELEVANT
DOCUMENTS WITH THE SECURITIES AND EXCHANGE COMMISSION AND LIFEMARK WILL FILE
WITH THE SEC A PROXY STATEMENT CONTAINING INFORMATION ABOUT THE MERGER.
UNITEDHEALTH GROUP AND LIFEMARK WILL MAIL A PROXY STATEMENT/PROSPECTUS TO
SHAREHOLDERS OF LIFEMARK. INVESTORS AND STOCKHOLDERS OF LIFEMARK ARE URGED TO
READ CAREFULLY THE REGISTRATION STATEMENT, THE PROXY STATEMENT/PROSPECTUS AND
OTHER DOCUMENTS TO BE FILED WITH THE SEC WHEN THEY ARE AVAILABLE. THE
REGISTRATION STATEMENT, PROXY STATEMENT/PROSPECTUS AND OTHER FILINGS WILL
CONTAIN IMPORTANT INFORMATION ABOUT UNITEDHEALTH GROUP, LIFEMARK, THE MERGER,
THE PERSONS SOLICITING PROXIES RELATING TO THE MERGER, THEIR INTERESTS IN THE
MERGER, AND RELATED MATTERS. INVESTORS AND STOCKHOLDERS OF LIFEMARK WILL BE ABLE
TO OBTAIN FREE COPIES OF THESE DOCUMENTS THROUGH THE WEBSITE MAINTAINED BY THE
SEC AT http:/www.sec.gov. INVESTORS AND STOCKHOLDERS OF LIFEMARK WILL ALSO BE
ABLE TO OBTAIN COPIES OF THE DOCUMENTS FILED BY UNITEDHEALTH GROUP FREE OF
CHARGE FROM UNITEDHEALTH GROUP BY MAILING A REQUEST TO UNITEDHEALTH GROUP
INCORPORATED, INVESTOR RELATIONS, UNITEDHEALTH GROUP CENTER, 9900 BREN ROAD
EAST, MINNETONKA, MINNESOTA 55343, TELEPHONE: (952) 936-1300. THE PROXY
STATEMENT/PROSPECTUS WILL ALSO BE AVAILABLE TO INVESTORS AND STOCKHOLDERS FREE
OF CHARGE FROM LIFEMARK BY MAILING A REQUEST TO LIFEMARK CORPORATION, INVESTOR
RELATIONS, 7600 NORTH 16TH STREET, SUITE 150, PHOENIX, ARIZONA 85020, TELEPHONE:
(602) 331-5150.

UNITEDHEALTH GROUP, LIFEMARK AND THEIR RESPECTIVE DIRECTORS, EXECUTIVE OFFICERS,
CERTAIN OTHER MEMBERS OF MANAGEMENT AND EMPLOYEES, EACH OF WHOM MAY BE
CONSIDERED PARTICIPANTS IN THIS TRANSACTION UNDER APPLICABLE SECURITIES LAWS,
MAY BE SOLICITING PROXIES FROM LIFEMARK'S STOCKHOLDERS IN FAVOR OF APPROVAL AND
ADOPTION OF THE MERGER AND THE MERGER AGREEMENT. A DETAILED LIST OF THE NAMES OF
UNITEDHEALTH GROUP'S AND LIFEMARK'S DIRECTORS AND EXECUTIVE OFFICERS ARE
INCLUDED IN THEIR RESPECTIVE PROXY STATEMENTS AND ANNUAL REPORTS ON FORM 10-K
FILED WITH THE SEC. A DESCRIPTION OF ANY INTERESTS THAT THESE PERSONS HAVE IN
THE MERGER WILL BE AVAILABLE IN THE PROXY STATEMENT/PROSPECTUS.