The company said that Mr. Witty had left the job for personal reasons. Stephen Hemsley, the company’s executive chairman, will replace him.
The chief executive of UnitedHealth Group, Andrew Witty, stepped down from his post for “personal reasons,” the company said in a statement on Tuesday.
The company also scrapped its financial forecast for this year because of higher than expected medical costs, saying only that it expected the company to “return to growth in 2026.”
After the announcement on Tuesday, UnitedHealth Group’s stock fell by more than 17 percent. Combined with a steep drop in April after its quarterly earnings came up short of expectations, the company’s stock has lost nearly half of its value over the past month.
Stephen Hemsley, the chairman of the company’s board of directors who served as chief executive from 2006 until 2017, will immediately succeed Mr. Witty, the company said.
Mr. Witty, who became chief executive in 2021, led UnitedHealth Group “during some of the most challenging times any company has ever faced,” Mr. Hemsley said in the statement.
UnitedHealth Group has faced turmoil recently, including the killing late last year of Brian Thompson, the chief executive of UnitedHealthcare, the group’s health insurance business, as well as a cyberattack on its payment systems.
Mr. Thompson was shot and killed in Midtown Manhattan on Dec. 4. Luigi Mangione, 27, was arrested in Altoona, Pa., five days later and charged with Mr. Thompson’s murder. Tim Noel, a long time employee of UnitedHealthcare, succeeded Mr. Thompson in January.
Mr. Mangione, who was not a UnitedHealthcare customer and who has pleaded not guilty to the murder charge, was carrying a statement when he was arrested that criticized what it called the health care industry’s “corruption” and “power games.”
Mr. Witty addressed some concerns about the health care industry in a New York Times Opinion piece shortly after Mr. Thompson’s killing.
“We know the health system does not work as well as it should, and we understand people’s frustrations with it,” Mr. Witty wrote. “No one would design a system like the one we have. And no one did. It’s a patchwork built over decades. Our mission is to help make it work better.”
UnitedHealth Group dominates nearly every segment of health care in the United States. In addition to the giant health insurer UnitedHealthcare, the company’s operations include its Optum subsidiary, which oversees some 90,000 physicians and clinics, and is a large pharmacy benefit manager.
In November 2024, the Justice Department and four Democratic state attorneys general filed an antitrust lawsuit against the company to try to block its $3.3 billion deal to take over Amedisys, a large home health company.
Mr. Witty, before joining UnitedHealth Group, was chief executive of the pharmaceutical company GlaxoSmithKline. From 2013 to 2017, he was chancellor of the University of Nottingham, his alma mater, in England.