OBJECTIVE To investigate the site, nature, cause, and severity of injuries in semi-professional rugby league players. METHODS The incidence of injury was prospectively studied in one hundred and fifty six semi-professional rugby league players over two competitive seasons. All injuries sustained during matches and training sessions were recorded. Injury data were collected from a total of 137 matches and 148 training sessions. Information recorded included the date and time of injury, site, nature, cause, and severity of injury. RESULTS During the two seasons, 1,694 playing injuries and 559 training injuries were sustained. The match injury incidence was 824.7 per 1,000 player-position game hours and training injury incidence was 45.3 per 1,000 training hours. Over 20% of the total training (17.4 per 1,000) and playing (168.0 per 1,000) injuries sustained were to the thigh and calf. Muscular injuries (haematomas and strains) were the most common type of injury sustained during training (22.0 per 1,000, 48.7%) and matches (271.7 per 1,000, 32.9%). Playing injuries were most commonly sustained in tackles (382.2 per 1,000, 46.3%), while overexertion was the most common cause of training injuries (15.5 per 1,000, 34.4%). The majority of playing injuries were sustained in the first half of matches (1,013.6 per 1,000, 61.5% v 635.8 per 1,000, 38.5%), whereas training injuries occurred more frequently in the latter stages of the training session (50.0 per 1,000, 55.3% v 40.5 per 1,000, 44.7%). Significantly more training injuries were sustained in the early half of the season, however, playing injuries occurred more frequently in the latter stages of the season. CONCLUSIONS These results suggest that changes in training and playing intensity impact significantly upon injury rates in semi-professional rugby league players. Further studies investigating the influence of training and playing intensity on injuries in rugby league are warranted.