Police say a medical condition may be behind a 67-year-old man's fatal crash near Chatham, Ont.

Allan Bonner's pickup truck drove off Highway 401 east of Chatham and ended up in a ditch Saturday at about 10:30 p.m.

The Stoney Creek, Ont., man was pronounced dead at the scene.

Police said an autopsy revealed a pre-existing medical condition that may have caused him to lose control of the truck.