Former CEO and longtime company leader Stephen Hemsley is resuming duties as chief executive at health care giant UnitedHealth Group in a surprise transition as the company’s recent financial woes have intensified.

Andrew Witty is stepping down as CEO for personal reasons, the company said, and will remain as a senior adviser to Hemsley, who has been serving as board chair since 2017.

The shakeup at the top of Minnesota’s largest company comes at a remarkably turbulent time, just over six months after the killing of UnitedHealth Group executive Brian Thompson on a public sidewalk in New York City and weeks after a one-day stock sell-off driven by deteriorating results wiped out $120 billion in the company’s market value.

Shares in the Eden Prairie-based company have fallen even further since the 22% stock plunge on April 17, which stemmed from higher-than-expected use of medical services in the company’s massive UnitedHealthcare health insurance business as well as within Optum Health, a fast-growing division that runs a national network of outpatient medical centers.

On Tuesday morning, UnitedHealth Group scheduled an impromptu call with investors to explain why it was discontinuing its financial forecast for the remainder of the year.

“The company suspended its 2025 outlook as care activity continued to accelerate while also broadening to more types of benefit offerings than seen in the first quarter, and the medical costs of many Medicare Advantage beneficiaries new to UnitedHealthcare remained higher than expected,” UnitedHealth Group said in a news release. “The company expects to return to growth in 2026.”

Hemsley, who was 72 years old in April, is an accountant by training. He joined the company as chief operating officer in 1997 and became president two years later, serving beside Dr. William McGuire, the visionary CEO who left the company in 2006 amid a scandal over stock option pricing. With McGuire’s departure, Hemsley stepped in as chief executive and held the job until 2017, a timespan that saw remarkable growth.

Witty, who was 60 years old last month, became chief executive of UnitedHealth Group in 2021 and shortly thereafter named Thompson as CEO for the company’s health insurance business. Previously the top executive at pharmaceutical giant GlaxoSmith Kline, Witty started his career at UnitedHealth by running the company’s Optum division, which sells a variety of health care services including pharmacy benefits management and health care data consulting.

Early in the COVID-19 pandemic, Witty stepped away from company leadership to work on the development of vaccines at the World Health Organization. After returning and becoming CEO, he was the public face of an enormous company during a remarkably difficult 2024, which included a Congressional grilling over how the company handled a cyberattack at its Change Healthcare subsidiary.

It was Witty who stepped on stage to suddenly close the company’s investor conference in December, as word spread of Thompson’s killing. In the following days, he issued a moving video message to workers, calling the tragedy immeasurably sad and profoundly shocking while encouraging colleagues to take time for family.

“We are grateful for Andrew’s stewardship of UnitedHealth Group, especially during some of the most challenging times any company has ever faced,” Hemsley said in a statement. “The board and I have greatly valued his leadership and compassion as chief executive and as a director and wish him and his family the best.”

Witty said in a statement: “Leading the people of UnitedHealth Group has been a tremendous honor as they work every day to improve the health system, and they will continue to inspire me.”

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