Abstract Objective—To determine the prevalence of tooth resorption in dogs and to evaluate whether a classification system for tooth resorption in humans is applicable in this species. Animals—224 dogs > 1 year old admitted for periodontal treatment or other dental procedures in 2007 Procedures—Full-mouth radiographs of all dogs were reviewed for evidence of tooth resorption. Tooth resorption was classified in accordance with radiographic criteria described for use in humans. Patient signalment and concurrent dental conditions were recorded and tabulated. Results—Tooth resorption was detected in 120 of 224 (53.6%) dogs and 943 of 8,478 (11.1%) teeth. The classification system for use in humans was applicable in 908 of 943 (96.3%) affected teeth. Tooth resorption was more frequent among older and large-breed dogs; no significant differences were found among sex categories. The 2 most common types of tooth resorption were external replacement resorption (77/224 [34.4%] dogs and 736/8,478 [8.7%] teeth) and external inflammatory resorption (58/224 [25.9%] dogs and 121/8,478 [1.4%] teeth). External cervical root surface resorption was detected in 13 of 224 (5.8%) dogs; external surface resorption was detected in 10 of 224 (4.5%) dogs, and internal inflammatory resorption and internal surface resorption were detected in 9 of 224 (4.0%) and 1 of 224 (0.4%) dogs, respectively. Internal replacement resorption was not detected. Conclusions and Clinical Relevance—The classification of tooth resorption in humans was applicable to tooth resorption in dogs. Resorption lesions, in general, and external replacement and external inflammatory resorption, in particular, were frequently detected in dogs.