It has been shown repeatedly that helmets significantly decrease head injury, death, and disability.'(Hagen, et al.,1979; Luna, et al., 1986; Oregon Motorcycle Accidents, 1960-1985; Accident Facts, 1986; Carr, et al., 1981; Heilman, et al., 1982; McSwain, et al., 1984; Bray, et al., 1985; Arizona Traffic Accident Summary, 1984; Baker, et al., 1980; Cairns, 1941; Cookro, 1979; Helmetless Motorcyclists Tniple Fatal Head Injury Risks, 1980; Luna, et al., 1984; Muller, 1980; Watson, et al., 1980; Rivara, et al., 1988) In the present study, the association of helmet use on the outcome of motorcycle crashes was studied. Because of the biased nature of the dataset, helmeted and unhelmeted patients were compared, controlling for severity of the crash as measured by a modified Injury Severity Score that excluded head injury. The risk of head injuries was nearly twice as high in non-helmeted riders. This study illustrates the increased likelihood of head injury when a helmet is not worn. In an era in which seat belts and child seats are mandatory in most states to protect passengers, it is difficult to understand why helmet laws are not universal.