Moving on the femoral srticular surface, the patella is doing a significant role in the patellofemoral mechanism as one of the most important components of the knee. The knowledge of patellar movement would be very helpful to understand the functional mechanism of the knee We studied the distance of patellar movement during the knee motion on the lateral X-ray view of 100 normal adult knees. The results were as follows :1. The average distance of patellar movement from full extension to full flexion of the knee was 8.4cm. 2. Patella moves average 1.7cm(20.2%) form 0° to 30° flexion, 2.6cm(31.0%) from 30° to 60° flexion, 1.7cm(20.2%) from 60° to 90° flexion, 1.3cm(15.5%) from 90° to 120° flexion and l.lcm(13.1%) from 120° to full flexion.