The purpose of this retrospective study was to evaluate the morphology of the intercondylar notch of the knee in 72 anterior cruciate ligament (ACL) intact group and 30 acute and chronic ACL tear group by plain radiographs and MRI, and to find the predisposing factors of ACL tear. The ACL tear group was divided into acute and chronic ACL tear group. In plain lateral radio-graphs, beta angle, angle between extension line from anterior cortical line of distal femur and from Blumensaat s line, was measured. In magnetic resonance imaging, the width of intercondylar notch (NB), the widest width of both femoral condyle (NW), intercondylar notch width from lower one third point of notch basal line (NB1), intercondylar notch width from upper one third point of notch basal line (NB2), depth of intercondylar notch from notch basal line (ND), and intercondylar angle which made from both end point of notch basal line and apex of intercondylar notch (alpha) were measured. Three groups were compared with each other by statistical analysis. Stastistically, the acute ACL tear group had narrow upper portion of intercondylar notch than chronic ACL tear group and more acute angle of roof of the intercondylar notch than intact ACL group. So in notchplasty, the upper one-third of intercondylar notch should be carefully widened. And after fixation of femoral interference screw, arthroscopic observation should be done whether reconstruced graft touchs the roof of the intercondylar notch during the extension of the knee.