The object of this study was to ascertain the consequences of meniscectomy performed because of meniscus injury sustained during sports. Out of 147 athletes meniscectomized from 1964 to 1973 a total of 142 were seen at follow-up. The median follow-up period was 4.25 (range 2.25-11.0) years. During the follow-up period 8 per cent (11/142) had further surgical treatment because of new knee injuries. At the time of follow-up, 15 per cent (20/131) of the patients who had undergone operation solely for the primary meniscus injury had given up sports because of knee complaints and 12 per cent (16/131) had restricted their sporting activities. There were no complaints in 46 per cent (60/131). In 79 per cent (56/71) of the patients who had complaints, these had started immediately after operation. The main trouble was a feeling of instability and pain on weight-bearing. The complaints correlated with the physical findings at follow-up. In 14 per cent (18/13) there was increased collateral instability of the knee. Considering also previous experimental studies, it is concluded that meniscectomy causes immediate functional changes in the knee which explain the complaints. There was no correlation between complaints and radiological osteoarthrosis.