The angiomyolipoma is a benign renal tumor composed of fat, smooth muscle, and abnormal blood vessels. The tumor often extends into the perinephric space and often is complicated by intratumoral or perinephric hemorrhage. The CT findings of 17 cases of angiomyolipoma were correlated with their pathologic findings and are described. CT scans usually demonstrate a large fatty mass intermixed with areas of tissue density which may represent nonfatty parts of the tumor or areas of hemorrhage. CT is more sensitive than plain films at detecting the fat within the angiomyolipoma. CT is also useful in identifying perinephric extension and hemorrhage. In those angiomyolipomas composed primarily of smooth muscle or in which intratumoral hemorrhage has obscured the fatty part of the tumor, the CT appearance is indistinguishable from other solid renal tumors.