The incidence of severe anterior cruciate ligament sprains was once only a third the current rate. This fact led the authors to believe a means to help reduce the risk of anterior cruciate ligament injury among skiers might be found. Using videotapes of the occurrences of anterior cruciate ligament sprains in alpine skiers and the data associated with more than 1400 anterior cruciate ligament injuries observed in a 22-year study, the authors identified two common mechanisms of anterior cruciate ligament injury. From this information, a study was designed to determine if training could help reduce the risk of anterior cruciate ligament sprains. During the 1993 to 1994 season, the on-slope staff from 20 ski areas participated in a training program involving viewing videotaped scenes where knee injuries occurred. Data from 22 ski areas, where staff were not exposed to the training, were assembled to form a control group. Data concerning anterior cruciate ligament injuries were collected from both groups for the three seasons 1991 to 1994. A total of 179 serious knee sprains were evaluated. Serious knee sprains declined by 62% among trained patrollers and instructors compared with the two previous seasons, but no decline occurred in the control group.