This study aimed to investigate the validity of disintegrative psychosis (DP) as defined in the ICD-9. The history of epilepsy in 13 subjects with DP was compared with that of 39 subjects with infantile autism (IA) who were matched for sex, age, IQ, and socioeconomic status (SES). The average follow-up time was 22 and 23 years (range 11 to 33 years). A significant difference was found between the DP and IA groups in terms of incidence of epilepsy, 77% versus 33% respectively. The peak period of onset of epilepsy occurred before puberty in both groups. Different types of epilepsy were seen, but the psychomotor variant accounted for 50% in the DP group, while 46% of the IA group had the psychomotor and 62% had the grand mal variant. The types are not mutually exclusive. Individuals without epilepsy had significantly higher IQ scores than those with epilepsy, but only within the IA group. The increased risk of developing epilepsy in the DP group is most likely a reflection of an underlying early brain pathology probably present in most individuals with DP. On the whole our findings can be seen as a contribution to the validation of DP as separate from IA, as these two conditions could be distinguished in terms of the way they develop with reference to epilepsy.