Compulsory military service entails a change in the patterns of physical activity of many conscripts, and an accompanying risk of musculoskeletal injury. The present study was carried out to determine the incidence and types of musculoskeletal injury among Norwegian conscripts, and their consequences in the form of sick leave and discharge from the service. The study population consisted of 6488 conscripts in all, drawn from the Army, the Air Force and the Navy. They were monitored through an initial 6-10-week period of basic military and physical training. Every injury for which a conscript had to consult a doctor was registered. Slightly more than every fourth Army, every fifth Air Force and every eighth Navy conscript suffered one or more injuries during basic training. Incidence rates for the Army, Air Force and Navy respectively were 15.3, 13.4 and 9.3 injuries per 100 conscripts-months. The sites of the majority of the injuries were in the lower limbs (63%). The most common types of injury were low back pain; overuse knee injuries; Achilles tendinitis; sprains of joint capsules or ligaments; and periostitis or compartment syndromes of lower leg. In the doctors' opinions, contributory or triggering causes of the injuries could be attributed to organized service activities in 67% of the cases. The number of days of partial or total sick leave as a result of injury amounted to 3.4% and 0.2% respectively of the total basic training period. Of Army, Air Force and Navy conscripts, 23%, 16% and 11% respectively had sick leave. Injury was also the direct cause of the discharge of 2.1% of the Army conscripts and 0.1% of the Air Force and Navy conscripts. The results of the study show that musculoskeletal injuries occur frequently during basic training and that injuries contribute to lost training time.