\s=b\Of 62 children seen at The Hospital for Sick Children, Toronto, who had tuberous sclerosis (TS), 58 had a history of seizures (developing during the first year of life in 37) and mental retardation was diagnosed in 51. Classic congenital hypopigmented patches were present in 42 and adenoma sebaceum occurred in 26 of the patients. Computed tomography (CT) is an essential diagnostic tool. We conclude that TS is more common than has been believed. Seizures are the most common manifestation of the disease and the hypopigmented patches, its first cutaneous manifestation, are present at an early age. When a positive diagnosis has been made, parents and siblings should be examined for signs of TS, keeping in mind the wide spectrum of findings in this condition; if no stigmata are present on examination, then a CT scan should be considered for parents of reproductive age so that proper genetic counseling can be given. (Am J Dis Child 1981;135:912-917)