A retrospective study was made of the injury records of a professional football team over a 12-year period to assess the incidence and severity of knee injuries. The importance of certain risk factors and the role of prophylactic knee bracing were evaluated. A higher overall incidence of knee injury was found than that reported for high school or college teams. The risk of injury was higher in games compared to practices, and on natural grass compared to synthetic turf. Certain player positions and lack of experience were also associated with higher risk. Following the introduction of prophylactic knee braces in 1984, the proportion of injuries considered major was significantly reduced, as was the incidence and severity of medial collateral ligament injuries. Such bracing, however, did not change the incidence of anterior cruciate ligament or meniscal injury. Continued use of prophylactic knee braces is recommended, along with further research and development into their design.