We have studied the accuracy of CT and MR in 9 oncocytoma and 6 angiomyolipoma, observed in our department from 1985 to 1991. The radiographic patterns of angiomyolipoma are due to the presence of fat in the tumors: on the CT angiomyolipoma appeared as low-density lesions (negative Hounsfield units) with an area of intermixed tissue density which represented myomatous and angiomyomatous elements. The infusion of contrast medium increased the difference between neoplasm and parenchyma because of the scarce enhancement of the angiomyolipoma. MR imaging of angiomyolipoma exhibited areas of high intensity signals on both T1 and T2 weighted images. The infusion of Gadolinium (1 mmol/kg) decreased the difference of signal intensity between angiomyolipoma and parenchyma so that the lesions appeared less clear. As far as oncocytoma diagnosis is concerned, neither CT nor MR appeared less clear. As far as oncocytoma diagnosis is concerned, neither CT nor MR appeared accurate and no specific pattern was identified. The "central stellate scar" was shown on CT in only 1 oncocytoma 7 cm large.