A 15-month-old bitch was presented for investigation of a two-month history of dysuria. Clinical signs had developed within one day of routine ovariohysterectomy. A rounded mass was palpable in the caudal abdomen which was shown radiographically to displace and compress the urinary bladder. On ultrasonography, the mass was composed primarily of pockets of hypoechoic fluid divided by hyperechoic septae; blood was obtained on fine-needle aspiration. The mass was surgically removed and the dog regained normal urinary function within a few days. Histopathological examination showed the mass to be an encapsulated haematoma, which is likely to have developed as a result of the ovariohysterectomy.