Mortality and neurological and mental outcome were studied in infants 28 days to 1 year of age with afebrile seizures not due to an acute postnatal injury. Cases were divided into four seizure types: infantile spasms: status epilepticus; and "others" (patients without spasms or status), generalized and partial. Mortality was studied in 334 cases, mental and neurological prognosis in 313 infants followed 1 year or more. Globally the prognosis was very poor even outside cases of infantile spasms. Mortality was higher and mental and neurological sequelae were more common in symptomatic than in cryptogenic cases. The highest mortality and greatest number of neurological defects were in status epilepticus and in "others" partial groups. Severely retarded subjects were more common in infantile spasms and "others" partial. The proportion of mentally normal patients, however, was no different according to ictal type. Mental and neurological prognosis was less unfavorable when the first seizure occurred at or over 6 months. A family history of epilepsy or febrile convulsions (21% of the cases in the whole series) was more common in the "others" subgroups, especially in the cryptogenic "others" (42%). The less unfavorable outcome obtained in cryptogenic "others" generalized with a positive family history.