A clinicopathologic study on 16 cases of renal angiomyolipoma is presented. Eleven were women and 5 men. The age ranged from 23 to 80 years with an average of 44.4. The course was from three days to one year. Abdominal mass, pain and hematuria were the main symptoms. Some individual cases were associated with tuberous sclerosis. Spontaneous rupture of the kidney was the principal complication often resulting in shock. The tumor was amenable to resection with a cure rate of 100% without recurrence, metastasis or infiltration of the large renal veins. The prognosis was good. B-type ultrasound and CT scan were helpful in the clinical diagnosis. Of 16 cases, 15 tumors occurred in unilateral kidney, in which the mass was usually located in one pole of the organ. The other tumor involved bilateral kidneys. The tumor was easily misdiagnosed as renal carcinoma by gross examination because of its being relatively large, yellow on the cut surface with hemorrhage and necrosis and often infiltrating tissues surrounding the kidney. Histologically, the tumor consisted of mature blood vessels, smooth muscles and adipose tissues. Sometimes, misdiagnosis of the renal angiomyolipoma with malignant change or angiomyoliposarcoma was made because of the active growth of the smooth muscle and adipose cells. In this paper, special emphasis is put in the discussion of the pathologic features and and causes leading to the misdiagnosis. Basing on long-term follow-up, it is suggested that angiomyolipoma of the kidney be a benign tumor of the hamartomatous nature.