Replacement lipomatosis of the kidney is the result of severe atrophy or destruction of the renal parenchyma often caused by calculous disease with secondary marked proliferation of renal sinus, renal hilus, and perirenal fatty tissue. The diagnosis is difficult to establish with conventional radiographic methods. Though ultrasonography may show highly suggestive findings, computed tomography seems to be the most accurate method in demonstrating the distinctive features of replacement lipomatosis, i.e. a rim of the destroyed renal parenchyma adjacent to a lipomatous mass with attenuation values similar to those of normal fat and calculi. This entity should readily be differentiated from fat-containing tumors in the kidney or its vicinity by computed tomography. When surgery is contemplated CT may also be of value to determine the extension of the fibrous fatty tissue relative to adjacent organs and possible abscess formation.