AbstractThe anterior cruciate ligament (ACL) is divided morphologically as well as functionally into anteromedial and posterolateral bundles.The changes in distance between femoral and tibial attachment sites of both bundles were measured throughout the full range of motion in ten formalin‐carbol preserved cadaveric knees.The femoro‐tibial distance (and thus the length) of the anteromedial bundle remains nearly the same throughout the full range of motion. The femoro‐tibial distance for the posterolateral bundle decreases with flexion; thus it becomes increasingly slack from 0° to 90° of flexion.For a truly functional replacement of the ACL, in which the roll‐glide motion of the knee joint is regained, isometric reconstruction of the anteromedial bundle is necessary. By utilizing the described method of intraoperative measurement, isometric positioning of the graft may be achieved. © 1993 Wiley