Proximal tibial osteotomy has proved to be a satisfactory surgical technique for the treatment of unicompartmental osteoarthritis and genu varum of the knee. After proximal tibial osteotomy, change of patellar height and patellar ligament length may contribute to altered biomechanics of the patellofemoral joint. The lateral radiographs of eighty kness (63 patients) that had a proximal tibial osteotomy were evaluated from Jan, 1983 to Jun, 1990. Authors analized relationship between the patella and patellar ligament using Insall-Salvati index and Blackburne-Peel index. 1. Using Insall-Salvati ratio, average preoperative patellar height was 0.94, average postoperative patellar height was 0.85. Seventy-two percent (58 knees) had a lower patella. 2. Using Blackburne-Peel ratio, average preoperative patellar height was 0.85, average postoperative patellar height was 0.82. Fifty-five percent (44 knees) had a lower patella. 3. In comparison between the patellar height at postoperative 6 weeks and at each follow up period, no change could be found. 4. Patellar height was more lowering in cases of excessive new bone formation at the area of patellar ligament insertion (4 knees). 5. No correlation could be found between wedge thickness and patellar height. Conclusively, early knee ROM exercise is needed to prevent patellar lowering due to shortening of patellar ligament that developed during the period of cast immobilization.