Marilyn Tavenner, administrator of the Centers for Medicare and Medicaid Services, announced her resignation — effective at the end of February — in an email to CMS staff today.
She did not specify her reason for leaving, but had been criticized for the unstable rollout of HeathCare.gov, the federal online insurance exchange, and last year acknowledged an "unacceptable mistake" in overstating the number of enrollees.
Tavenner directed programs that provide health care coverage for more than 100 million Americans. During her time at CMS, Medicare programs expanded in 27 states and the District of Columbia.
Deputy administrator Andy Slavitt will take over as acting administrator upon Tavenner's departure. Slavitt joined CMS in July 2014 with a directive to fix the faulty exchange. He was formerly a top executive at a unit of UnitedHealth, one of the nation's largest insurers.
Slavitt will officially be acting administrator of CMS, a role Tavenner held from 2010 to 2013, when she was confirmed as administrator by a 91-7 Senate vote.
Kevin Counihan will oversee HealthCare.gov when Slavitt moves to the top CMS position.