Keira Knightley and Scarlett Johansson have posed naked for a photo shoot.

They appear on the cover of Vanity Fair's annual Hollywood issue, with designer Tom Ford.

Ford is the issue's guest art director reports IOL.com.

Ford said he hadn't planned on joining in, but did so when Wedding Crashers star Rachel McAdams, 29, backed out.

"She did want to do it, and then when she was on the set I think she felt uncomfortable, and I didn't want to make anybody feel uncomfortable" Ford told ABC's Good Morning America.

After the photoshot Johansson and Knightley, who had never met before, reportedly kissed each other goodbye, Knightley said: "Lovely to meet you. I'll see you again some time...naked I'm sure."

Johansson replied: "Very nice meeting you...in the most intimate way."

The magazine also features Angelina Jolie posing in a bathtub and a fully clothed George Clooney as a director filming a large cast of women wearing skin-tone underwear.