This study examined tibial tuberosity radiolucency (TTR) on radiographs to better understand its causes and significance. Radiographs (n = 675) of canine stifle joints were reviewed; 21.5% were found to have TTR proximal and caudal to the tibial tuberosity. Radiolucency (ie, dark areas) ranged from small and faint to larger and well-defined. For dogs that had bilateral stifle radiographs available (n = 52), radiolucency was bilateral in 96.2% of cases. Radiolucency size did not correlate with stifle disease. Breed size was significantly associated with TTR; toy-, small-, and medium-breed dogs were more commonly affected. Young age and medial patellar luxation (MPL) were also significantly associated with TTR. TTR may be caused by a retained cartilage core and may be associated with MPL. A cause-and-effect relationship could not be established, and further studies to identify the cause for this radiographic lesion are warranted.