AbstractAn 8‐year‐old, neutered, male rottweiler presented for evaluation of pollakiuria and a large abdominal mass. Computed tomographic evaluation revealed a large caudal abdominal mass occupying the pelvic inlet, obscuring the prostate, as well as concurrent hepatic nodules. A prostatectomy, urethrotomy and liver biopsies were performed. Pollakiuria resolved, and the patient was discharged on Day 4 post‐operatively. Histopathological evaluation was consistent with primary prostatic hemangiosarcoma with no metastasis. The dog acutely decompensated 26 days post‐operatively and was re‐evaluated. Peritoneal effusion prompted computed tomographic re‐examination. An amorphous mass in the region of the previous prostatectomy site and changes to the previously normal urinary bladder wall and colon were identified. Concurrently, contrast extravasation from a urinary bladder wall defect was present. Uroabdomen was confirmed, suspected secondary to neoplastic infiltration. The dog was humanely euthanased. This is the first report to describe the computed tomographic appearance, surgical management and short‐term outcome of canine primary prostatic hemangiosarcoma.