Our objective was to identify patterns of injury and illness and develop possible preventive strategies for competitors in a wilderness multisport endurance event. Using a prospective observational cohort study during the Winter Classic, a 2-day wilderness multisport endurance event held in rugged alpine terrain in Victoria, Australia, we sought details of demographics, pre-, intra-, and postrace injuries and illness. We employed chi-squared tests and iterative multivariate analysis. There were 33 respondents with 26 (78%) aged between 26 and 35 years. Seven (21%) developed symptoms consistent with exposure, and three (9%) developed asthma during the race. Competitors in the marathon pairs class had a 50% risk of exposure vs 12% for the individual class (p = 0.031). The number of times raced, nonsteroidal anti-inflammatory drug use, and increasing age were the other independent significant predictors of exposure. Twenty-three (70%) of the competitors were injured at some time during the race. The day 1 run was more commonly associated with injuries than other stages (39% injured, p = 0.0037). Increased amounts of training, previous musculoskeletal problems, and increased number of previous race attempts were all significant independent predictors of injury. Most competitors (67%) suffered musculoskeletal problems after the race, these typically being of the thighs and calves, but only two competitors required time off from their normal activities. We concluded that injuries in wilderness multisport endurance events are common, particularly in the run stages. These injuries are usually minor, but their frequency makes major injury an ever-present risk. Both injury and illness are more frequent in those who compete while carrying injuries. These events are high risk for the development of injuries and illness and require a high level of competitor preparation and readily available medical support.