Sixteen patients with old knee ligament injuries and symptoms of instability or pain were treated with a 3-month thigh muscle strength training program. Nine patients had a tear of the anterior and six patients a tear of the posterior cruciate ligament. One patient had a tear of both cruciates. Knee function was determined with a knee scoring scale, and thigh muscle strength with a Cybex-II dynamometer before training, after 1 and 3 months of training, and at a late follow-up after 2 years. Ten patients who increased their quadriceps strength by more than 15 per cent increased their score over 30 per cent. Three patients who showed a minor increase in strength did not increase their score significantly. Three patients did not increase their strength at all. All of these admitted a reluctance to train. Four patients, all with anterior cruciate ligament tears, were operated on after the 3-month training period. All four patients increased their strength. Two of them increased their functional score also, but they strove for a very high activity level and were therefore operated on. The other two patients had no symptomatic relief and were therefore also operated on. Improvements in muscle strength and knee function were unchanged at the 2-year follow up. Before planning a knee ligament reconstruction, a period of strength training is recommended.