The optimal femoral insertion or footprint for an anterior cruciate ligament (ACL) graft is the anatomic site. This study was designed to determine the radiographic localization of the femoral insertion of the ACL on a lateral roentgenogram using a quadrant method. Ten human cadaveric knees with intact ACL were dissected. The most anterior, posterior, proximal, and distal borders of the femoral insertion of the ACL were marked with K-wires that were shortened at the bone level of the intercondylar fossa. A roentgenogram was obtained in the strictly lateral position. The end of the K-wires determined the projection of the femoral ACL insertion on the lateral roentgenogram. The center of the radiographically marked area was defined as point K, then four distances were measured on the lateral roentgenogram: distance t (representing the total sagittal diameter of the lateral condyle measured along Blumensaat's line), distance h (representing the maximum intercondylar notch height), distance a (representing the distance of point K from the most dorsal subchondral contour of the lateral femoral condyle), and distance b (representing the distance of point K from Blumensaat's line). Distance a is a partial distance of t and distance b is a partial distance of h, and distances a and b are expressed as length ratios of t and h. The center of the femoral insertion of the ACL was located at 24.8% of the distance t measured from the most posterior contour of the lateral femoral condyle and at 28.5% of the height h measured from Blumensaat's line. Based on these results, the ACL can be found just inferior to the most superoposterior quadrant, which means in anatomic terms it is localized from the dorsal border of the condyle at approximately a quarter of the whole sagittal diameter of the condyle and from the roof of the notch at approximately a quarter of the notch height. By using this radiographic quadrant method combined with fluoroscopic control during surgery, we were able to reinsert the ACL at its anatomic insertion site. This method is independent of variation in knee size or film-focus distance, easy to handle, and reproducible.