It has been suggested that an increased tibial slope and a narrow inter-condylar notch increase the risk of anterior cruciate ligament (ACL) injury. The aim of this study was to establish why there are conflicting reports on their significance. It was a retrospective and comparative case-control study out of 80 patients divided into two groups. Group 1 consisted of 40 patients with unilateral ACL rupture. Group 2 involved 40 control subjects. We measured the Tibial Slope on lateral knee X-ray by three methods. The geometry of the Inter-condylar Notch was evaluated by the notch width index, the notch shape index and the notch height index on Schuss radiography and on MRI. The Group 1 average Tibial Slope was above the Group 2 average regardless of the method of measurement, with a statistical difference significant (P< 0.05). Mean notch width index and mean notch shape index in-group 1 were lower than those in Group 2, with a statistically significant difference (P < 0.05). Ninety-five percent of our Group 1 had at least one of these two factors. Our study showed that a high Tibial Slope and narrow inter-condylar notch geometry were risk factors for ACL rupture. Sports medicine must screen for those factors, especially in pivot sports. The surgeon should take consideration of these factors both in the surgical technique and in the post-operative follow-up.