Two half-brothers with tuberous sclerosis (TS) presented with polycystic kidneys in early childhood, before the classical stigmata became apparent. Their father shows no evidence of the disease. The older boys subsequently developed adenoma sebaceum at nine years and the younger boy developed infantile spasms. Hypertension occurred in both cases but neither showed evidence of renal failure. Extensive renal cyst formation in TS is rare, but when it does occur it differs from both infantile and adult-type polycystic disease. TS should be considered in the differential diagnosis of renal enlargement, haematuria and hypertension in childhood.