Despite increasing interest in the anatomic importance of the meniscal insertion, little information is available regarding the relationship between the tibial slope and the meniscal insertion. Lateral radiographs and MRI sagittal images from 100 healthy and young patients were used in this study. Patients without deformation, meniscal pathology, or previous surgery to the ipsilateral knee were included in this study. We measured the angle between a line tangent to the medial and lateral tibial slope and the proximal tibial anatomical axis using a lateral radiographs. We also measured the angle between the tangent line to the medial and lateral tibial insertion of the meniscus and the proximal tibial anatomical axis using sagittal MRI images. The measurements were carried out twice by two observers. Inter-observer reliability ranged from 0.98 to 0.99 and intra-observer reliability ranged from 0.83 to 0.94. For each observer, the mean differences between measurements made using radiographs and MRI images were 16.4 degrees and 16.4 degrees on the lateral side, respectively, and 6.0 degrees and 5.9 degrees on the medial side, respectively. There was a statistically significant difference between measurements made using radiographs and MRI images (p < 0.001). However, the Pearson's correlation coefficient between the measurements made using radiographs and MRI images did not show a linear correlation. The measurements of posterior slope on lateral radiographs images and meniscal insertion on sagittal MRI images were reproducible and reliable. Differences in measurements ranged from 15 degrees to 17 degrees on the lateral side and from 5 degrees to 6 degrees on the medial side, with 95% confidence intervals. However, there was no statistical correlation between the measurements made using lateral radiographs and MRI images.