A sample of 304 fatally injured motorcyclists (60 helmeted and 244 unhelmeted) is analyzed for the incidence, location, and mechanisms of basilar skull fracture and the influence of protective safety helmets on these injuries. The relationships of basilar skull fractures to head impacts, head and neck motion and helmet use are examined, and the literature on basilar skull fractures is reviewed and summarized. Findings include a statistically significant reduction of basilar skull fractures among helmeted riders, but these injuries are not excluded by helmets. Hinge fractures of the middle cranial fossa were found in both helmeted and unhelmeted riders, and hyperextension from frontal head impact is often responsible for basilar skull fractures in both helmeted and unhelmeted motorcyclists.