Leiomyosarcoma of the kidney is a relatively rare tumor. We have found 25 cases in the literature, which we have reviewed in the accompanying Table. We are presenting another case, with an attempt to clarify the biology of this type of tumor. Report of a Case Present Illness. —A 51-year-old white man was known to have had heart disease since 1946. After three years of angina pectoris, he developed what was considered to be a posterior wall infarct. In September, 1953, he was treated for advanced right and left ventricular failure. Since then, he had been maintained on digitalis and acetazoleamide (Diamox), and he continued to have recurrent angina. Recently, he noted pain in the right upper quadrant, occurring more often at rest than on exertion and unrelated to dietary indiscretion. The pain radiated into the chest, right shoulder, and right scapular region. He entered the Mount Sinai Hospital on