The 41-year-old former "Parenthood" star said he was molested at age of seven by an 18-year-old neighbour, reported US magazine.
He said the abuse was "minimal," but had a profound effect on him.
"It took me 12 years to tell anyone. And then all that time, I was like, a) 'It's my fault,' as generic as that is ... 'and I'm gay, I must have manifested this because I'm secretly gay.' I had all these insane thoughts for 11 years or 12 years," he added.
Shepard, who has two daughters with wife Kristen Bell, has been open about his struggles with addiction. The actor said it is close to impossible to stay away from addiction if one is molested.