The actress revealed she was molested at age six, and raped at 12 during the kickoff of the advocacy group for animal rights, Friday at the Cannes Film Festival.
"I did not have an easy childhood. Despite loving parents, I was molested from age six by a female babysitter," the 46-year-old star said, according to the Daily Mail.
Then six years later, the former Baywatch star said an encounter with a male acquaintance turned violent.
"I went to a friend's boyfriend's house and his older brother decided to teach me backgammon, which led into a back massage, which led into rape," she said. "He was 25 years old and I was 12."
After that, a boyfriend "decided it would be funny to gang-rape me with six friends," Anderson said, adding she "wanted off this earth."
But she says that her love of animals helped her heal.
"My affinity with animals saved me, they came to me naturally. The trees spoke to me. I wasn't sure why I was alive – a burning question, a quest," she said.
"My loyalty remained with the animal kingdom. I vowed to protect them and only them. I prayed to the whales with my feet in the ocean, my only real friends until I had children."
The gathering was attended by about 200 people, including Anderson's husband Rick Salomon.
After she spoke, the star wrote on Twitter, "My speech at launch of my Namesake foundation. I want people to know - they can overcome and prosper with love."
The actress's rep has not yet responded to E!'s requests for comment.