Previous reports have failed to demonstrate a statistically significant adverse effect of acute ethanol intoxication in the well-resuscitated trauma patient. In the present study the prevalence of acute alcohol intoxication and its effect on outcome was analyzed in a homogenous population of young, previously healthy motorcycle accident victims (N= 134). The incidence of intoxication was 25%. The intoxicated cyclists were at fault for the accident 50% more often than the nonintoxicated cyclists and were found to wear helmets one third as frequently. Furthermore, the protective effect of helmet use as seen in the nonintoxicated group was lost in the intoxicated group, who sustained head injuries twice as frequently. Only patients with critical head injuries died and, although the ISS levels of those dying were similar in the two groups, the mortality following the critical head injury was twice as high among intoxicated patients (80 vs. 43%). Overall, the intoxicated group had a fourfold increased mortality rate. Thus, although intoxicated motorcyclists comprised 25% of the total population, they represent a mere 9% of the helmet-wearing population, and, in contrast, 39% of the severely head-injured victims and a majority (57%) of the mortality rate.