The former vice president, 62, who has emphatically denied the allegations, sat down Thursday with detectives in San Francisco, Portland TV station KATU reports.
A spokesperson for Gore declined to comment.
Therapist Molly Hagerty alleges Gore demanded sexual favors and made "unwanted sexual contact" with her during a massage in his Portland, Ore., hotel room four years ago.
Officials said they were reopening the investigation after detectives looking into the alleged incident this past year failed to notify high-ranking officials that they were dropping the case.
Gore and his wife Tipper, 61, split in June after 40 years of marriage. Tipper does not believe Haggerty's allegations, says a friend, who adds that "they played no role whatsoever in their decision to separate."