When Sally Field was just 14, her stepfather would call her into his bedroom alone.

The following contains details of sexual assault which may be distressing. For 24-hour support, please call 1800 RESPECT.

Sally Field is known for her roles in some of the most iconic films of all time, including Forrest Gump and Mrs. Doubtfire.

But the 71-year-old actress has a devastating past.

Speaking to Lisa Wilkinson on The Project about her new memoir, In Pieces, the actress spoke about being sexually abused by her stepfather as a child.

“Your stepfather did let you down in the worst possible way,” Wilkinson said. “How difficult has it been to write about what he did to you?”

Sally Field spoke to Lisa Wilkinson on The Project. Image: Channel Ten.

Field said the writing process was emotionally challenging.

"[The process was] hugely emotional, because reliving what my childhood was with my stepfather is hugely complicated and emotional," Field said.

"Because he was so lovable at the same time that he was threatening," she added.

In her memoir, Field recalls that when she was 14 years old, her stepfather, stuntman Jock “Jocko” Mahoney, would call her into his bedroom alone.

“I knew… I felt both a child, helpless, and not a child. Powerful. This was power. And I owned it. But I wanted to be a child — and yet.”

Mahoney died in 1989. Field didn't tell her mother about the abuse until after she starred in Lincoln in 2012.

The Oscar-winning actress also spoke to Wilkinson about her complicated relationship with her biological father, who ignored her.

"When my mother married my stepfather he was big, and bold, and loud, and affectionate and dangerous, very troublesome," she said.

"Whereas my real father, I was completely ignored," she added.

The memoir, In Pieces, took Sally Field seven years to write.

If you have experienced sexual assault and are in need of support, please call 1800 RESPECT. That’s 1800 737 732. Help is available 24 hours a day, seven days a week.