We reviewed 46 cases of renal angiomyolipoma covering the period from 1977 to 1997. Eight cases were associated with tuberous sclerosis and one with lymphangiomyomatosis. Histologically, the lesions were most often classic with the three usual components, i.e., mature adipose tissue, thick-walled blood vessels, and smooth muscle. Seven cases were particularly misleading: three cases were entirely adipose mimicking liposarcoma: two cases had an exclusively smooth-muscle component, one mimicking lymphangiomyomatosis and one with epithelioid cells; another case had a monophasic epithelioid pleomorphic component ("REON": renal epithelioid oxyphilic neoplasm) and proved to be fatal; and another case was associated with collecting duct carcinoma. The immunohistochemical profile showed the coexpression of alpha-smooth-muscle actin and HMB45. Our study is the first to show positivity of estrogen and progesteron receptors or both in more than 25% of cases. Of 35 cases with follow-up information, only one patient died of malignant spread of angiomyolipoma.