We describe two cases of unusual presentation of tuberous sclerosis with cystic renal involvement. A 19-month-old white male who was initially misdiagnosed as having polycystic kidney disease of "adult-type" developed petit mal seizures and small "ash-leaf" depigmented areas, raising a suspicion of tuberous sclerosis. Computerized tomography (CT) of the brain revealed periventricular calcifications, confirming the diagnosis of tuberous sclerosis. A 15 3/4-year-old black female with tuberous sclerosis showed acceleration of renal failure. Computerized tomography scan of the abdomen showed cystic lesions of the kidneys. In young children with cystic renal involvement but a negative family history of tuberous sclerosis or polycystic kidney disease, a CT scan of the brain should assist in the diagnosis. A CT scan or ultrasound examination of the abdomen will differentiate cystic renal lesions from angiomyolipoma of the kidneys.