UnitedHealth CEO Andrew Witty is stepping down for personal reasons and the nation's largest health insurer suspended its full-year financial outlook due to higher-than-expected medical costs.

UnitedHealth said Tuesday that Chairman Stephen Hemsley will become CEO, effective immediately.

Hemsley was UnitedHealth Group CEO from 2006 to 2017. He will remain chairman of the company’s board. Witty will serve as a senior adviser to Hemsley.

UnitedHealth said that it suspended its 2025 outlook as medical costs of many Medicare Advantage beneficiaries new to UnitedHealthcare were higher than expected.

UnitedHealth anticipates returning to growth next year.