On a Zoom call with reporters, Ripken, who turns 60 next week, said he was diagnosed in February during a routine checkup and underwent surgery in March.
"I don't know if I'm the only one that's ever did it in and out on the same day with this kind of surgery," Ripken told reporters. "But the good news is it has a real happy ending. The cancer was all contained in the prostate. They did a pathology report afterward and confirmed that that was the case. I've since had a three-month test to see if my PSA [prostate-specific antigen] was undetectable, and it was, so we can make a case that all the cancer was contained and it's all out now."
Due to his age, Ripken said he wasn't alarmed when his PSA was high during the initial doctor visit. As a precaution, a biopsy was performed, and the results "came back iffy," he said.
Ripken received the news during the early days of the coronavirus pandemic, and he wanted to get the surgery done before the hospitals were overrun.
"The weird part is, when it first happens to you, I kept thinking, 'I don't want to tell anybody,'" Ripken said. "It's almost like there's something wrong with you. I wouldn't say the Iron Man [nickname] contributes to it, but I was the kind of person who was thinking, 'OK, I'll just keep this a secret.'
"But the longer you deal with it and you understand the outcome has been favorable and positive, the reason I'm letting it slip out now is I want to use the opportunity to help other people who struggle with that decision and encourage other people to go get their regular exams, get their tests."
Ripken, who holds the major league record for most consecutive games played, retired in 2001 and was inducted into the Baseball Hall of Fame in 2007, his first year of eligibility.
His announcement came on a call with local media in preparation for the 25th anniversary next month of Ripken surpassing Lou Gehrig's consecutive-games streak.
"We all know people that have had different cancers, and you kind of wonder, 'How would you feel if it happened to you?'" said Ripken, whose father, Cal Ripken Sr., died of lung cancer in 1999. "I know what that feels like now."