In human bladder cancer patients, ultrasonography is extensively used not only to identify tumor masses but also to evaluate tumor size, shape, echogenicity, location, and degree of tumor invasion into the bladder wall. The information revealed by ultrasonography delineates the tumor's biological features and facilitates prediction of prognosis. However, in veterinary medicine the feasibility of using ultrasonography for these purposes has not been fully investigated. In this retrospective study, we reviewed cases of dogs with histologically confirmed bladder mass lesions, including transitional cell carcinoma (n = 22) and polypoid cystitis (n = 5), to determine whether ultrasonography could reliably predict bladder wall involvement. By following patients with transitional cell carcinoma until death, we also determined whether ultrasonographic tumor size, shape, echogenicity, and mass location were related to prognosis. Wall involvement as revealed by ultrasound was significantly (P = 0.00005) associated with histological muscular layer involvement with a sensitivity of 93% (95% Confidence interval, 79-98%) and specificity of 92% (95% Confidence interval, 76-98%). Ultrasonographic wall involvement (P = 0.03, vs. noninvolvement), heterogeneous mass (P = 0.02, vs. homogeneous mass), and trigone location (P = 0.01, vs. other locations) characteristics were significantly associated with shorter survival times in transitional cell carcinoma cases. Findings indicated that ultrasonographic characteristics such as wall involvement, heterogeneous mass, and trigone location could be reliable prognostic indicators in canine transitional cell carcinoma. (C) 2013 American College of Veterinary Radiology.