Primary leiomyosarcoma of the kidney is an extremely rare disease. No single case of primary renal leiomyosarcoma was reported at National Taiwan University Hospital during 1995-2010. Here, we report the case of a 74-year-old woman who presented with intermittent lower abdominal pain for 2 months. A heterogeneous tumor was found in the left kidney. The clinical presentation suggested renal cell carcinoma. A diagnosis of leiomyosarcoma was made based on the pathological examination. The patient underwent radical nephrectomy. No
distant metastasis was noted. No adjuvant chemotherapy or radiotherapy was provided after surgery.