Eighteen consecutive patients with acute spontaneous perinephric hemorrhage were examined with computed tomography (CT) (n = 18), ultrasonography (US) (n = 15), and angiography (n = 9). Renal cell carcinoma was found in 10 patients; angiomyolipoma, three; and segmental renal infarction, arteriovenous malformation (AVM), hemorrhagic cyst, abscess, and idiopathic hemorrhage, one each. Initial CT examinations demonstrated the extent of hemorrhage in all cases and a distinct mass in 12 (67%), with CT characteristics suggestive of the correct diagnosis in 11. In the other six patients (33%), a discrete mass was not seen at initial CT, and in five cause of hemorrhage was not clear. Two of the five underwent follow-up CT, which correctly demonstrated carcinoma in both. Overall, CT findings suggested the correct diagnosis in 14 patients (78%). US was sensitive for detection of an abnormality but nonspecific as to its nature. Angiography demonstrated unsuspected AVM in one patient, segmental renal infarction seen at CT in one, but only one of five carcinomas suspected at CT. Data from this study suggest that CT is the most valuable examination for patients with spontaneous renal hemorrhage.