Few studies have examined the rate of injuries for those attending summer camps and other recreational facili ties. We developed a surveillance system for the 1985 National Boy Scout Jamboree to determine the inci dence, nature, and cause of injuries among participants. To characterize the more severe injuries among scouts, we monitored referral visits to an onsite Army hospital. During the 9 day event there was a total of 179 injuries requiring referral visits among the 24,885 scouts, for an overall incidence of 8.5 injuries per 10,000 person- days. Twenty-eight injuries (16%) involved fractures. Ten injuries required hospitalization, for an overall rate of 0.5 per 10,000 person-days. Thirty-six (20%) of the injuries occurred during six organized athletic activities. Of these six, two new Jamboree activities, the bucking bronco and bicycle motocross racing, had the highest event-specific rates, 14.4 and 11.4 injuries per 10,000 participants, respectively. These two events also ac counted for one-third of all fractures. In contrast, there were no firearm-related injuries among the 32,616 par ticipants in riflery events. This simple and inexpensive surveillance system provided a mechanism for monitor ing activity modifications, as well as useful information for the selection and planning of organized activities at future Jamborees and similar recreational events.