Former CEO and current chairman Stephen Hemsley is stepping back into the top job following the abrupt resignation of Andrew Witty, UnitedHealth said.

May 13 (UPI) -- UnitedHealth Group announced Tuesday CEO Andrew Witty will step down, citing "personal reasons." Witty will leave the role of CEO and be replaced by Stephen J. Hemsley, effective immediately.

As CEO for more than a decade, Stephen Hemsley built up UnitedHealth Group, now a $400 billion healthcare behemoth. With his return to the top job, the company will learn whether his playbook still works.

UnitedHealth Group announced the surprise exit of CEO Andrew Witty on Tuesday and suspended its 2025 forecast due to surging medical costs, sending its shares down more than 10% premarket.

A group of investors this week filed a proposed class-action lawsuit against UnitedHealth Group, alleging that the company withheld information following the murder of UnitedHealthcare CEO Brian Thompson last December.

UnitedHealth Group (NYSE: UNH) today announced the appointment of Stephen J. Hemsley as its chief executive officer, effective immediately, following Andrew Witty’s decision to step down as CEO for personal reasons.

The lawsuit, which seeks class action status, alleges that UnitedHealth and its executives didn’t properly warn investors about how the killing of UnitedHealthcare CEO Brian Thompson would affect its business.