This study examines the effect of the tibial slope on the anterior cruciate ligament lesion (separately on the lateral and medial tibial condyle). The study consisted of 33 matched pairs of patients divided into two groups: an examined group with a diagnosed ACL lesion, and a control group with diagnosed patellofemoral pain. The patients were matched on the basis of four attributes: age, sex, type of lesion (whether it was profession-related), and whether the lesion was left- or right-sided. Measurements were carried out by radiography and MRI. In the examined group, the lateral tibial plateau was significantly greater than in the control group (P < 0.001), and the medial tibial plateau had lower tibial slope values than the control group; however, the difference was not statistically significant (P = 0.066). In both groups, the difference between the slopes on the lateral and medial plateaus was statistically significant (P < 0.001). In relation to ACL intact patients, population with ACL rupture have greater tibial slope of the lateral condyle. The greater tibial slope of the lateral tibial plateau may be the factor that leads to the injury of the anterior cruciate ligament. Compared to the medial plateau, the population with ACL rupture have a greater tibial slope on the lateral plateau, while the population of the intact ACL have greater tibial slope on the medial plateau. The tibial slope of the medial and lateral condyle should be compared separately because the values obtained from the two sets of data were different, revealing apparently opposing effects on the ACL lesion.