Idiopathic renal replacement lipomatosis is a rare condition in which the renal parenchyma, especially the renal sinus is replaced with adipose tissue with increase in perirenal fat. We report a case of renal replacement lipomatosis presenting as a renal mass clinically. The computed tomography scan revealed low density and nodular masses of adipose tissue within the renal parenchyma. The differential diagnosis before surgery was angiomyolipoma, lipoma, and xanthogranulomatous pyelonephritis. After the histological examination and extensive literature search, the diagnosis of renal replacement lipomatosis was made. It is a rare entity and may be missed if not considered due to lack of experience, so we hope that more urologists, radiologists, and pathologists become aware of this entity and recognize it.