Renal angiomyolipomas, the most familiar of the renal hamartomas, are well known to radiologists, despite being uncommon and of limited clinical importance, because angiomyolipomas represent one of the few lesions for which a specific diagnosis can be achieved on the basis of radiologic findings in the majority of cases. Because of the diversity in the relative amounts of various cellular components and because of the occasional association with acute hemorrhage, the radiologic features of angiomyolipomas can be somewhat varied. At sonography, angiomyolipomas appear echogenic with acoustic shadowing. At computed tomography (CT), these lesions typically appear as well-marginated, small (< 5 cm in size), cortical masses of predominantly fat attenuation with heterogeneous soft-tissue attenuation interspersed throughout. Some angiomyolipomas are larger and poorly marginated because of hemorrhage. Typical angiomyolipomas are largely composed of fat; those uncommon tumors without demonstrable fat cannot be radiologically distinguished from renal cell carcinoma. Renal leiomyoma, a lesion that pathologically overlaps with angiomyolipoma to some degree, has a quite different imaging appearance (ie, homogeneous, without detectable fat) that cannot be distinguished from malignant renal lesions.