During the period 1975-1981, 48 persons were operated on at Tampere University Central Hospital for an acute knee ligament sports injury. Their mean age was 31.6 years. A total of 40 patients had a postoperative follow-up ranging from 2 to 7 years (average 41 months). The number of operations increased greatly during the observation period: in 1980-1981, 29 operations (60%) were performed. Of all the injuries, 29 (60%) occurred in the winter season (January-March). Cross-country skiing was the cause in nearly half of the cases (23), and 21 of these were spare time sports injuries involving mainly middle-aged women (15). According to the questionnaire and clinical and radiological reexamination, the patients injured in spare time sports did not differ significantly from the patients with no sports injury in respect to the amount, quality, or position of the pathological changes in the knee. However, the whole group of top-level or competitive sportsmen had significantly better healing results than the other patients. Slippery cross-country skis made from glass fibers seem to be dangerous, especially for older female spare time skiers. Competitive sportsmen's better healing results are obviously based on their younger age, better muscular performance, and higher motivation, and better possibilities for rehabilitation.