BACKGROUND:Establishing the incidence of injury is the first step in initiating injury prevention strategies. There is a lack of research on injury in Irish adolescents and this study paves the way for further injury prevention research, by implementing a prospective cohort study. PURPOSE:To establish the epidemiology of injury in male adolescents in Irish secondary schools in one academic year. METHODS:452 male 4th and 5th year adolescents (aged 15.62±0.70 years) took part in a prospective epidemiology study for one academic year. Any injury sustained during training or competition resulting in restricted performance or time lost from play was assessed weekly by an athletic rehabilitation therapist. An injury report form was completed to ensure standardisation of the injury description. RESULTS:5.16 injuries per 1,000 hours were noted, with 35.6% at risk of injury and 27.9% of injured participants at risk of sustaining another injury that school year. Competition injuries (16.91 injuries per 1,000 hours) were more common than training injuries (2.63 injuries per 1,000 hours). Lower limb injuries predominated (73.1%) with knee (17.9%), ankle (13.5%) and hamstring (11.7%) injuries most common. Strains (29.4%), sprains (20.8%), fatigue-induced muscle disorder (14.5%) and contusions (13.1%) were frequent. Injuries were primarily minor (0–7 days) (41.6%), followed by severe (>22 days) (39.7%) and moderate (8–21 days) (18.7%). CONCLUSION:Injuries are common in adolescents in Irish secondary schools and the development and implementation of injury prevention strategies are required.