The findings at ultrasonography (US), CT, and angiography in 13 patients with renal angiomyolipomas were compared with histologically determined proportions of fatty, myogenic, and vascular components. The angiomyolipoma was composed mainly of fat in 4 cases, half of fat in 2, mainly of myogenic tissue in 4, and was hemorrhagic in 3. US showed high echogenicity in 10 patients, while CT demonstrated attenuation values of fat in 3 tumors with mainly fat tissue but gave non-specific findings in the other cases. The angiographic findings were considered specific for angiomyolipoma in 2 out of 11 cases (18?). Low fat content and hemorrhagic areas caused diagnostic difficulties at both US and CT. The diagnostic algorithm for renal angiomyolipoma is discussed.