In 1986, 23 patients with renal angiomyolipomas as part of tuberous sclerosis were assessed by ultrasonography. In 1991, 20 patients in this group were reexamined with special attention paid to the renal pathological condition. Ultrasonography was performed by the same radiologist who performed the examination in 1986. Of 20 patients 7 had severe hemorrhage necessitating hospital admission (5 had a renal lesion larger than 3.5 cm. in diameter). In 2 patients the exact diameter of the renal angiomyolipomas could not be determined and they underwent nephrectomy. Three patients underwent successful selective embolization of the bleeding angiomyolipoma. One patient died. The hemorrhage resolved spontaneously in 1 patient and treatment was not feasible. In 4 patients the lesions increased in size between 1986 and 1991. Based on these results there is a relationship between the size of the angiomyolipomas and the risk of bleeding. Renal angiomyolipomas larger than 3.5 cm. in diameter have a substantial risk for severe hemorrhage. Some angiomyolipomas show progression. Periodic followup is mandatory every 6 months. For angiomyolipomas larger than 3.5 cm. in diameter an aggressive approach is advised. Selective embolization is the initial method of choice.