Former Sen. Barry Goldwater, 78, was admitted to a hospital here, but a spokesman said Goldwater asked that no information be released on his condition.
Jim McAllister, a spokesman for St. Luke's Medical Center, said Wednesday: "He's a patient. What he's in for, I don't know."
McAllister said he believed Goldwater had been admitted either Tuesday night or Wednesday morning.
Last week, Goldwater told a Kingman student who had invited him to a May 23 graduation that he would be unable to attend because of knee surgery. At the time, Goldwater said he expected to spend about seven weeks recovering.
Former Goldwater aide Doris Berry said the surgery was necessary because of a knee injury Goldwater suffered as a college football player.
The veteran Republican, who retired in January after 30 years in the Senate, was the GOP presidential candidate who lost to Democrat Lyndon B. Johnson in 1964.