In a prospective study, we determined whether preinjury and postinjury differences existed in the mood state and self-esteem of competitive athletes. The influence of severity of injury, gender, level of participation in sports, and type of sport on these dependent variables was also measured. Among 238 male and 38 female athletes from hockey, basketball, baseball, and volleyball teams, 36 sustained 43 injuries. Significant postinjury increases were noted for depression (P < 0.0001) and anger (P = 0.0012), whereas vigor (P < 0.0001) was significantly less after injury. When the 36 injuries were classified, 27 were minor or moderate (nonparticipation in sports for only one or two weekly assessments), and 9 were severe (nonparticipation for three or more weekly assessments). When a stepwise multiple regression equation was used to predict the scores for postinjury depression, the only significant predictor was the severity of injury (F = 8.48 [1, 34]; R2 = 0.30; P = 0.0063). Of the following physical and psychosocial variables--level of participation, type of sport, age, previous injury, preinjury stress, gender, mood state scales, and self-esteem--only level of participation (P < 0.0001) and type of sport (P = 0.0004) were predictors of injury. The significant preinjury and postinjury differences in mood state suggest that postinjury mood disturbances reported in previous studies are likely attributable to the occurrence of injury, are related to the severity of injury, and do not merely reflect a disturbed preinjury mood.