Hemsley, 72, had led the company for more than a decade until 2017 and is re-taking the reins following a series of setbacks.

UnitedHealth's stock has plunged nearly 40% year-to-date as the company has battled a series of crises. Can the healthcare giant turn it around? Seeking Alpha analysts weigh in.

Stephen Hemsley ran UnitedHealth Group for more than a decade. It's a different company after four years with Andrew Witty in charge.

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.

UnitedHealth Group surprises investors with what its CEO said was an "unusual and unacceptable" quarterly earnings miss, and lowers its outlook for the full year due to higher-than-expected medical costs, sparking a more than 20% selloff in shares that reverberated across the sector.

"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. "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.