"My illness has progressed beyond my doctors' expectations of cure," Killebrew said in a statement released by the Twins. "I am very comfortable taking this next step and experiencing the compassionate care that hospice provides."
Killebrew, who is 74, announced last December that he had been diagnosed with cancer. At the time, he said that he anticipated "a full recovery."
Killebrew played 22 seasons in the major leagues, beginning with the Washington Senators in 1954, when he was 18 years old. He moved with the franchise to Minnesota in 1961, and played with the Twins through 1974. Killebrew then played one season with the Royals before retiring.
Killebrew, an 11-time All-Star who was the American League's Most Valuable Player in 1969, was voted into the Hall of Fame in 1984, in his fourth year on the ballot.
He ranked fifth all time with 573 homers when he retired in 1975.
In retirement, Killebrew was a familiar and welcome figure around the Twins, a pleasant man who never seemed to demand special treatment, Knobler notes.
In his statement Friday, Killebrew thanked fans for the concern they've shown since the announcement that he has cancer.
"I look forward to spending my final days in comfort and peace with [wife] Nita by my side," he said.