The purpose of this study was to evaluate the relative risk of anterior cruciate ligament injury in female versus male midshipmen at the United States Naval Academy. From 1991 to 1997, we recorded the incidence of anterior cruciate ligament injury during intercollegiate athletics, intramural athletics, and military training. The subjects were male and female varsity athletes, coed intramural athletes, and participants in military training consisting of the obstacle course and instructional wrestling. All patient data were collected at the time of injury. Records filed at the intramural sports office, along with a questionnaire completed by coaches and trainers, were used to estimate midshipmen exposures. Results showed that in intercollegiate soccer, basketball, and rugby, women had a relative injury risk of 3.96 compared with men. In coed soccer, basketball, softball, and volleyball, the women's relative injury risk was 1.40 compared with men. In military training, women had a relative injury risk of 9.74 compared with men. In comparing overall annual anterior cruciate ligament injury rates among midshipmen, we found that women had a relative injury risk of 2.44 compared with men. We concluded that female midshipmen have an increased relative risk of anterior cruciate ligament injury as compared with men in intercollegiate athletics, basic military training, and throughout their service academy career. This increase was not statistically significant at the intramural level of athletics.