Children are the most frequent victims of bicycling accidents. Among fatal accidents, head injury is the most common cause of death. Because bicycling helmets may reduce the risk of serious head injury, this study was undertaken to determine the frequency with which children and adolescents in various age groups use bicycle helmets. Students were observed arriving at four elementary schools, three junior high schools, three senior high schools, and one university campus. The number of students riding bicycles and the percentage wearing helmets were noted. Of 108 elementary schools bicyclists, only two (1.85%) wore helmets. None of 103 junior high bicyclists and only two of 107 (1.86%) senior high bicyclists wore helmets. Ten percent (15/150) of university bicyclists wore helmets; this is a significantly higher rate than in the other age groups (chi 2 = 10.27, P less than .01). The failure of school-aged children to wear bicycling helmets represents a potentially serious health hazard. Pediatricians and family physicians have a unique opportunity to provide education to families and communities about the importance of using helmets.