Yours Mine and Ours (1968)
Since first seeing Tim Matheson's perfect backside flashed briefly in Animal House, I wondered where else his it may have made an appearance... I believe Tim had just three nude scenes, showing his butt again in a great scene in 1984's Impulse and another brief flash as he dives naked into a swimming pool in 1195's Midnight Heat.
One of his earliest skin scenes wasn't a nude scene, but the 19 year old Matheson did have a shirtless scene in 1968's Yours Mine and Ours. In the scene, Time is inspected by Tom Bosley after being drafted. Tim was briefly shirtless a couple of other times in the film that also featured Ben Murphy in a small role.
A Little Sex (1982)
Despite the teasing title, there was no nudity from Tim in A Little Sex, but plenty of shirtless scenes.
Midnight Heat (1995)
The softcore thriller 'Midnight Heat' features plenty of boobs, but we do get a brief glimpse of Tim as he jumps into the pool. \Tim was approaching 50 during the making of the film, and, was still looking mighty fine!
The best view of Tim's toosh is in 1984's Impulse co-starring Meg Tilly.
Animal House (1978)