Three dogs and one cat with lymphoma affecting the urinary bladder are reported and the findings on abdominal radiographs and ultrasound are described. Mural lesions representing lymphoma affecting the urinary bladder were identified ultrasonographically in all animals. The most common complications associated with urinary bladder lymphoma were hydronephrosis and hydroureter. In two patients contrast radiography was necessary to detect leakage of urine in the peritoneal and retroperitoneal space. The radiographic and ultrasonographic signs were similar to those reported with other urinary bladder neoplasms; hence urinary bladder lymphoma could not be distinguished from the more common urinary bladder neoplasms, such as transitional cell carcinoma. It is important to include lymphoma in the differential diagnosis of urinary bladder wall thickening and mural mass in dogs and cats.