Thesis (Ed.D.)--Boston University / Background: Season-ending injuries, particularly those to the anterior cruciate ligament (ACL), continue at a high-rate in many sports, particularly ski racing. Although many factors are thought to contribute to this injury rate in both genders, no study has looked at possible psychological influences. Hypothesis: There is a form of post-traumatic stress disorder (PTSD) that affects athletes after seeing someone in their own sport sustain a serious injury. The result could be a decrease in performance both on and off the mountain. In the worst-case scenario, this change in tactics could result in injury to themselves, representing an "injury contagion". Study Design: Case-control study; Level of evidence, 3. Methods: Students at four Eastern ski academies were studied for 3 consecutive years (2002-2005). The subjects ranged in age from 13-19 and consisted of 277 men (60.3%) and 182 women (39.7% ). When a subject sustained a season-ending injury, a peer group of that subject was tested for both psychological and performance effects. The results of this testing was compared to previous baseline testing and a similarly constructed control group from an academy without such an injury. Results: There were twelve season-ending injuries sustained over the three-year period. Significant data results were obtained from one aspect of the psychological testing of the peer group. There was a trend toward a possible "injury contagion" i.e. injury to a member of the peer group soon after injury to a teammate. Conclusions: Although the results of this study were inconclusive in establishing the existence of an "injury contagion", there were data to establish a psychological affect on some athletes after injury to one of their teammates. Clinical Relevance: Although a teammate's injury did not measurably effect performance and only showed mild evidence of a possible injury contagion, there were significant psychological affects noted in female subjects. School personnel should be trained in basic counseling techniques specific to this problem.