We report the computed tomographic (CT) features of urinomas caused by ureteral injuries which are often not clinically suspected, causing delay in diagnosis. CT studies of 12 patients with ureteral injury were reviewed. Ureteral injuries were iatrogenic in 9 patients and traumatic in the remaining three. CT was performed between 2 and 139 days (average = 33 days) after the insult. The most common presenting symptoms were severe abdominal pain and fever. All CT studies were performed before and after intravenous contrast administration. In 11 of 12 cases, delayed scanning was added 15 min to 5 h later. The sites of injury were the proximal ureter in two patients, the middle ureter in three, the distal ureter in two, and the ureteral anastomosis in five. The urinomas appeared as confined water-density fluid collections in seven patients, as free fluid (urinary ascites) in two, and as both in three. Extravasation of contrast from the ureter was observed on early scans in six patients and on delayed scanning only in the other six. The density of the opacified urinoma measured 80-200 HU. Ipsilateral hydronephrosis was observed in seven patients. Ureteral injuries were treated conservatively in eight patients and surgically in four. Ureteral injuries after iatrogenic or penetrating trauma often are diagnosed with considerable delay. The presence of ascites or localized fluid collections in symptomatic patients after abdominal surgery or penetrating trauma should raise the possibility of a ureteral injury and prompt delayed scanning.