A retrospective study of spontaneous remission and long-term outcome in patients with infantile spasms. The spontaneous remission rate and long-term outcome in 44 patients with infantile spasms not treated with hormonal drugs were studied. The cumulative spontaneous remission rate during the first 12 months after onset of infantile spasms, as determined by retrospective analysis, was as follows: 1 month, 2%; 2 months, 2%; 3 months, 5%; 4 months, 7%; 5 months, 9%; 6 months, 11%; 7 months, 11%; 8 months, 14%; 9 months, 16%; 10 months, 18%; 11 months, 25%; 12 months, 25%. The average age at follow-up was 80 months. Nine percent of patients had normal development or only mild impairment. The remainder showed various degrees of retardation. These data should be useful in the design and interpretation of therapeutic drug trials in patients with infantile spasms. 