Twenty-eight consecutive, skeletally immature patients (9.9-15.0 years of age at the time of injury) with total rupture of the anterior cruciate ligament (ACL) were followed up for 3-5 years. The aims of the study were to monitor the natural course of conservative treatment, to identify variables relevant to failure of conservative treatment, and to evaluate an over-the-top procedure for ACL reconstruction by using the semitendinosus tendon and avoiding the physes. The patients were interviewed according to Lysholm knee score and Tegner activity level. Knee laxity and muscle torque were measured. Five patients insisted on immediate reconstruction. Twenty-three patients were sent to a 3-month rehabilitation program. Sixty-eight percent of the patients, who made an attempt with conservative treatment, had been operated on at follow-up. The patients not operated on were younger at injury and had a lower activity level at follow-up. The surgical procedure improved objective and subjective knee function, but there was a correlation between high activity level and a low Lysholm score.