In this 3-year prospective study, the incidence and nature of injuries incurred by a professional rugby league football club were investigated. During the 1989, 1990, and 1991 season games, 141 injuries occurred throughout the first, second, and under-21 age teams, which resulted in players missing subsequent games. The incidence of injury was 44.9 per 1000 player-position game hours, which is high when compared with other sports. Of these injuries, 37.6% were classified as minor, 34.8% as moderate, and 27.6% as major. The classification was based on the number of subsequent games missed: minor injuries caused a player to miss one game; moderate, two to four games; and major, five or more games. Ligament and joint injuries comprised 53.9% of all injuries, and the knee was the most common area injured (24.1%). The commonest specific injuries were to the medial collateral ligament of the knee and to the groin musculotendinous unit (10.6% each).