2. The average congruence angle was decreased with progressive flexion (from 5.5°to -5.3°in the control group, from 25.0°to 1.2°in the patient group;p<0.001). 3. The average patellar tilt angle was between 15.7°and 18.1°in the control group and between 9.0°and 10.7°in the patient group(p(0.001). 4. The average lateral patellofemoral angle was between 6.9°and 4.4°in control group and between -3.6°and 4.6°in patents group(p<0.001). 5. The patient group could be classified as 3 types. 17 of the 41 kness belonged to type I, 16 to type II and 6 to type III. 2 of them had no malalignment. 6. The ratio of the femoral trochlear depth was increased with progressive flexion (from 10% to 14.7% in the control group, from 9% to 14.2% in the patient group). Type II and type III of above classification were significantly different from type I and controls in the femoral trochlear depth (p<0.001). These findings mean that type II and type III were associated with much shallower trochleae. 7. The ratio of the femoral condylar width was decreased with progressive flexion(from 47.5% to 46.3% in the control group, from 47.9% to 46% in the patient group). 8. According to Wiberg classication of patellar shape, type II was the most common in control and patients group. There were no differences in the type distribution between both groups. 9. The criteria of malalignment could be determined, which were patella tilt angle less than 7°congruence angle greater than 0°at 15°of knee flexion and lateral patellofemoral angle less than 0°at full extension of the knee. 10. The specificity of C.T. scan for the diagnosis of the patellofemoral malaignment was 0.93 and sensitivity was.0.95. The specificity of roentgenogram(Merchant view) was 0.97 and sensitivity was 0.29. 11. Based on the above results the patellofemoral pain can be diagnosed more accuratly by using C.T. scan. In addition, C.T. scan may be very helpful in planning the treatment and understanding the pathomechanics of the patellofemoral pain.