The series consisted of 26 patients operated on in 1972-1978 for chondromalacia patellae. The patients were followed up an average of 4.6 years after the operation. The operation involved one knee in 21 patients, both knees in 5. The primary operation was carried out for lesions of the articular cartilage of the patella alone in 18 cases (in 6 of these a second operation was necessary) and for a biomechanical disturbance of the patellofemoral joint in 13 cases. Degenerative changes of the patellar cartilage were observed at anatomo-pathological examination in 29 of 31 knees. On average, the patients' symptoms were alleviated after the operation, but comparison of different types of operation showed a statistically significant improvement only after operations that modified the biomechanics. The results confirm the view that symptoms originating in the patellofemoral joint often are due to biomechanical disturbances of this joint and the extensor system of the knee, and that the removal of injured cartilage alone is not sufficient.