The aim of this study was to characterize the type and severeity of acute injuries occurring in Finnish orienteerers in 1987 to 1991. The study is based on the orienteering license insurance records accounting for 2189 orienteering injuries during 69268 person-years of exposure in active orienteerers. Of these orienteerers, 73.0% were male; 73.5% (N = 1608) of all injuries occurred in males, so the injury rate was similar in males and females. The rate was highest in orienteerers 20 to 24 years of age and lowest in children. Injuries occurred most commonly during May to September (78.9% or all injuries), the months which include the orienteering competition season, and were more common during competitions (59.8%) than during training. A high number of the injuries occurred during weekends (58.9% of injuries) including 68.1% of all competition injuries and 44.9% of all training injuries. The lower limbs were involved in 1611 (73.6%) of cases, the ankle (28.7%) and the knee (23.2%) being the two most common injury locations. Sprains, strains and contusions were the most common injuries. Wounds were proportionally more common in males than in females while ankle sprains were more common in females. Fractures, seven open and 94 closed, accounted for 4.6% of injuries; they were most common in the hand/wrist/forearm (N = 44) and ankle (N = 16), and were more frequent during competition (62.3%) than during training. The most important areas for preventive measures seem to be the ankle and the knee.