History, signalment, and tumor location are important factors used to diagnose canine transmissible venereal tumor (TVT). There should be a high index of suspicion of this disease in any intact, sexually active dog, with a recent travel history that presents with a genital mass. Clinical signs, signalment, and cytological features are often sufficient for making a diagnosis of TVT, however, biopsy and histological examination may be necessary in cases with an atypical presentation. This case report outlines the workup and treatment of a dog diagnosed with TVT, a rarely encountered tumor at the Cornell University Hospital for Animals.