OBJECTIVE To determine the frequency of injuries requiring medical attention among mountain bike racers at endurance races (6 hours or greater in duration) versus traditional cross country races (less than 6 hours duration) and to determine the medical support available at races. METHODS A survey was developed to determine participants' experience level, previous injuries, and demographic information. An additional survey was completed by injured riders to determine injuries and treatment received. The number of medical providers, their level of training, and the supplies available was determined. RESULTS The endurance riders had more years of mountain biking experience, averaged more hours of riding per week, and had fewer injuries requiring medical attention in the past year than the riders in the races. Of the cross-country riders, 7.2% were injured during the race, and 4.7% of endurance racers were injured. There was no increased risk of being injured in a race over an endurance race (odds ratio 1.6, 95% CI [0.50, 2.92]). Lacerations and abrasions were the most common injuries in both events. Head injuries, eye injuries, and blisters were only reported in the endurance events. Endurance events were more likely to have medical assistance available. CONCLUSIONS There was a greater percentage of riders reporting injuries in the cross-country races. It is possible that many of the endurance racers did not report injuries, continuing to ride or taking care of their own injuries quickly. Both events tended to have similar types of injuries and, therefore, both events most likely need similar medical support.