In a prospective study 21 consecutive patients were followed up for an average of 6 years after partial tear of the anterior cruciate ligament (ACL) diagnosed by clinical examination and arthroscopy. The ACL tear was treated conservatively and associated lesions were sutured. At followup a knee function score was recorded. The maximum possible score was 100 points. The mean score at followup was 93 +/- 6 points. All patients were classified as good or excellent. Three knees were unstable at followup, but the score was not impaired. With a partial tear of the ACL the course is benign and the long-term result good, in contrast to total ruptures of ACLs. It is, therefore, important to make an accurate diagnosis in order to choose the proper treatment.