We report the first prospective study on the incidence of motorcycle accidents of the world's foremost motorcycle road-racing venue, the Isle of Man. Between 1989 and 1991 there were six meetings during which over 2500 riders took part. Racing on essentially normal country and town roads, the motorcycles can reach speeds in excess of 306 km/h and the average lap record is now 198 km/h. During the study, 175 motorcyclists were injured and 16 were killed (9.1 per cent). The most common injury patterns were soft tissue injury (114 riders), head injury (52) and fractures/dislocations (188), of which one-third were open. The injuries sustained were more frequent and of a greater severity than recreational motorcycling. The casualty rate was 15 times, and the fatality rate 87 times the national figures. Of the 16 fatalities only seven reached hospital alive, despite the use of helicopter air ambulance, and 14 had serious head injuries. No fatality was thought to have been avoidable on review. There were no cervical spine injuries and only two major abdominal injuries. Of the injured riders, 93 (56 per cent) were admitted and there were 170 surgical procedures undertaken on 54 riders.