The aim of this study was to determine if the radiographic assessment of patella alta using the patellar tendon:patella ratio can be applied to sagittal MR images of the knee. Sagittal T1-weighted MR images of 46 knees were reviewed with corresponding radiographs. After lengths of the patella and patellar tendon were measured on the lateral radiographs and on the sagittal mid patellar images, the tendon:patella ratios were calculated. We found the mean tendon:patella ratio on radiographs to be 1.0 +/- 0.2 (SD) and on MR imaging, 1.1 +/- 0.1. These two values were not significantly different (p = .01) and had good-to-excellent correlation (r = .7). We found no statistical difference between the sexes on either radiographs or MR imaging, nor did we find statistical differences on MR imaging between the tendon:patella ratios of straight and wavy patellar tendons. As on radiographs, patellar height can be reliably assessed on sagittal MR imaging using the patellar tendon:patella ratio. On sagittal MR imaging, patella alta is suggested at values greater than 1.3 (1.1 + 2 SD).