Tuberous sclerosis (TS) represents a relatively frequent inherited disorder of the skin and neurological tissues. Defects of other organs may also be present, but subjects differ significantly in their individual involvement. Usually, white leaf - shaped macules, even though most subtle, are the first precocious sign of the disease in young patients. Other signs tend to appear when the patient grows older. Visceral disorders include renal angiomyolipomata; clinical behavior of these solid tumors is almost always benign. Sometimes the renal lesions present themselves as polycystic kidneys, and may be the earliest sign and the only manifestation of TS, such as the case here described. This unusual form of renal involvement may be a severe potential complication of TS for the possible blood hypertension, recurrent urinary sepsis and chronic renal failure. It is of the utmost importance to search for the classical stigmata of TS in any patient who has cystic renal enlargement as only apparent abnormality. Careful inquiry into the family history cannot be overemphasized. The authors believe that, failing availability of adequate therapy for TS, the role in genetic counseling is to provide as much informations as possible to enable the involved family to make an intelligent decision about future children.