Renal angiomyolipomas were present in 23 out of a series of 38 patients with proven tuberous sclerosis (60.5%). Multiplicity and bilateral localization of combined renal angiomyolipomas were important differences between this category and the isolated, usually solitary, angiomyolipomas. One of the parents of a patient with tuberous sclerosis had small renal angiomyolipomas without signs of tuberous sclerosis. This indicates that renal angiomyolipomas might be a forme fruste of tuberous sclerosis. Two patients with suspected isolated renal angiomyolipomas proved to have tuberous sclerosis. From this study we can conclude that multiple angiomyolipomas, or a combination of a single renal hamartoma with one of the signs suggestive of tuberous sclerosis, warrant a thorough examination to exclude tuberous sclerosis.