The short- and long-term outcome and special problems of 24 children with infantile spasms and tuberous sclerosis (TS) was studied. The diagnosis of TS is frequently missed: white spots on the skin have to be carefully looked for. In the present study, these spots were always found, and calcifications or hypodense areas of the brain were revealed by CT scans before one year of age. In addition to epilepsy, manifestations of TS included: giant cell astrocytoma, iridic heterotopia, cardiac rhabdomyoma, brain cysts, polycystic kidneys with severe arterial hypertension, retinal phakomas, angiofibroma and white spots on the skin. Long-term outcome was poor. None of the children had normal intelligence and all but one had epilepsy, which was often intractable. Behavioural problems were common. The prognosis, in terms of later intelligence, epilepsy and behavioural problems, was worse than in those with 'idiopathic' infantile spasms or in those with simultaneous neurological disorders. An early diagnosis of TS in patients with infantile spasms clarifies the prognosis and avoids some of the hazards of ACTH therapy. TS children have a high relapse rate after ACTH therapy, so prolonged courses may be indicated.