93 knees in 74 patients between 9 and 20 years of age were operated because of patello-femoral instability. In 76 cases, it was due to an intractable patello-femoral syndrome and in 17 cases one or several episodes of patellar dislocation had occurred. Treatment consisted, after failure of physical therapy, 14 times in a leavering of vastus medialis with a lateral capsular release and medial capsularrophy. In 71 cases it was associated to a medial transfer of the patellar ligament. Results were studied in 85 knees after an average follow-up of 6 years. 45 knees were completely symptomless, an excellent result. 34 knees remained with some kind of pain and 6 patellae redislocated. It is concluded that the transfer of the patellar ligament should be associated to the dynamic realignment achieved by the vastus medialis transfer for better results.