UnitedHealth Group's new CEO Steve Hemsley Monday apologized for the company's recent earnings underperformance, and vowed it will curb rising costs in its insurance business and optimize quality in its health services moving forward.

"We are well aware we have not fulfilled your expectations or our own. We apologize for that performance, and we're humbly determined to earn back your trust and your confidence," Hemsley said at the company's annual shareholder meeting.

Hemsley replaced former CEO Andrew Witty in May, following the healthcare giant's first earnings miss since 2008. Along with the appointment, UnitedHealth suspended its earnings outlook, as it weighed higher-than-expected costs in its Medicare Advantage unit for adults 65 and older and people with disabilities.