Defense Secretary Lloyd Austin was transported to the hospital on Sunday to be seen for "symptoms suggesting an emergent bladder issue," the Pentagon said in a statement.
On Sunday afternoon, he transferred duties of his office to Deputy Secretary of Defense Kathleen Hicks.
"The Chairman of the Joint Chiefs of Staff, the White House, and Congress have been notified," Pentagon Press Secretary Maj. Gen. Pat Ryder said in a statement.
Austin was still hospitalized as of Sunday evening, the Pentagon said.
The Sunday afternoon announcement came just weeks after Austin was diagnosed with prostate cancer in early December and hospitalized on Dec. 22 for a related procedure.
Austin transferred his authority to Hicks the following day, but neither she nor President Biden knew that Austin was in the hospital. He was hospitalized again on Jan. 1 for complications from the first procedure. Biden didn't learn of the hospitalization until Jan. 4.
Members of Congress blasted Austin for concealing the diagnosis and treatment from the president and lawmakers, prompting the 70-year-old to hold a press conference earlier this month and apologize.
"We did not handle this right and I did not handle this right," Austin said. "I should have told the president about my cancer diagnosis. I should have also told my team and the American public, and I take full responsibility."
The Pentagon said Austin's security detail took him to the Walter Reed National Military Medical Center Sunday afternoon.
In a joint statement later that day, trauma medical director Dr. John Maddox and Center for Prostate Disease Research of the Murtha Cancer Center director Dr. Gregory Chesnut said that Austin had been admitted to the critical care unit and it was unclear how long he would be hospitalized.
"The current bladder issue is not expected to change his anticipated full recovery," they said. "His cancer prognosis remains excellent."