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Renal leiomyoma Tuberous sclerosis Abstract The renal lesions characteristic of tuberous sclerosis are angiomyolipoma and cysts, with the former considered to be more common. Other renal tumors are rarely associated with tuberous sclerosis. Here we present a tuberous sclerosis patient with a renal leiomyoma which was detected incidentally during the investigation of fever of unknown origin. Dr. A. Tsujimura, Department of Urology, Osaka National Hospital, Hoenzaka. 2-1-14, Chuo-ku, Osaka 540 (Japan) Introduction Tuberous sclerosis is an inherited autosomal dominant disease characterized by mental retardation, epilepsy, adenoma sebaceum, and hamartomas of the bone, brain, eyes, lungs, heart, and kidneys. Most of the renal tumors associated with tuberous sclerosis are angiomyolipomas (renal hamartomas). We report an extremely rare case of tuberous sclerosis associated with renal leiomyoma, a rare benign tumor arising from smooth muscle in the renal capsule, renal cortical vessels, or renal pelvis. located in the upper pole of the left kidney. The mass showed a low echogenicity on ultrasonography and a low density on computed tomography with contrast enhancement (fig. 1). Left renal arteriogra-phy revealed that the mass contained numerous vessels and microaneurysms, while T2-weighted magnetic resonance imaging showed that it was of low intensity. Partial nephrectomy was performed under the diagnosis of a benign tumor causing left hydronephrosis and pyelonephritis. The resected specimen contained a homogeneous gray-white tumor, which was 6 cm in diameter (fig. 2). Histo-logical examination of the entire tumor revealed a benign lesion composed of spindle cells arranged in interlacing fascicles without nuclear atypia or mitotic figures. There was no fatty component and none of the vascular changes which would suggest angiomyolipoma. The histological findings, including desmin staining (fig. 3), led to a diagnosis of typical leiomyoma.