We studied motorcycle-related injuries in Tehran from 23 August 1999 to 21 September 2000 in 6 hospitals. Data were obtained from the trauma registry and questionnaires completed by trained physicians. Of a total of 8500 patients with trauma injuries, 1332 were motorcyclists, with a male to female ratio of 15:1. Of these, 1226 patients were driving the motorcycle at the time of the accident and 75 were pillion passengers. Crashes involving another vehicle were the commonest kind of accident (72.5%). Helmet use was noted in only 8.6% of cases. There were 28 fatalities and head injuries were the prominent cause of death. Of those who died, none had been wearing a helmet at time of the crash. Only 2.7% of helmeted riders sustained a head injury, compared with 11.2% of riders without a helmet. The commonest musculoskeletal injury was fracture: tibial fracture with 509 cases (49.8%) comprised the largest proportion.