Using data from the National Pediatric Trauma Registry, this study examined the characteristics of bicycle-related head injury, factors related to the presence of head injury, and different outcomes of head injury up to the time of discharge. Of the 2,333 patients ages 0 to 14 years who were admitted to trauma centers because of bicycle-related injury during 1989 through 1992, more than one-half (54%) sustained head injury, predominantly concussions and skull fractures. With adjustment for age, sex, and motor vehicle involvement, children who had pre-existing mental disorders, who did not wear a helmet at the time of injury, or who were injured on roads had a significantly increased likelihood of sustaining head injuries. Patients with a head injury were four times as likely as patients with no head injury to be treated in intensive care units, and were almost twice as likely to develop complications. Head injury was associated with an increased risk of inhospital fatality and high prevalence rates of communication and behavior impairments at discharge. Although it is urgent to increase helmet use substantially by child bicyclists, special attention should be paid to high-risk groups, such as children with mental disorders and children who are likely to ride in traffic.