To understand bicycle injuries and determine how to prevent them, we designed prospectively a descriptive study of bicycle-crash-related admissions in July 1993 to 10 major Ohio hospitals that admit child trauma patients. All patients studied were under the age of 16. In the 52 cases (38 male, 73%), impact with another vehicle accounted for 23 (44%) crashes. Of these crashes, only three (13%) were caused by definite motor vehicle operator error, and all 20 (87%) of the remaining motor vehicle-bicycle collisions were caused by bicyclist error, including 10 (43%) caused by bicyclists failing to yield properly at an intersection. Head injuries were the primary cause of morbidity in 29 (56%) cases. No child was wearing a bicycle helmet at the time of the crash. Efforts to reduce childhood morbidity from bicycle-related crashes should focus on helmet education and safe riding skills.