Bruce Jenner, the Olympic gold medalist and member of the Kardashian family, ended months of speculation Friday night when he announced during an ABC television special that he identified as a woman and was making the transition from male to female.

“For all intents and purposes, I am a woman,” he told Diane Sawyer in an interview. “People look at me differently. They see this macho male, but this female side is part of me, it’s who I am. I was not genetically born that way.”

The announcement made him among the highest-profile people to publicly come out as transgender. For the purpose of the interview, Mr. Jenner said he preferred the pronoun “he,” and Ms. Sawyer called him Bruce. He said that he had been undergoing hormone therapy for a year and a half but had not made up his mind about reassignment surgery. He declined to provide the name he might use during or after his transition, citing privacy concerns.

Rumors about a possible transition have been trumpeted for months by tabloids and celebrity magazines.