The long-term prognosis of childhood-onset epilepsy has rarely been studied in a general population. We examined the long-term medical, educational, and social outcomes in individuals with a history of childhood-onset epilepsy aged 20 years or older in a defined area of Japan. Furthermore, the patients' recognition of epilepsy as well as the parents' concerns about the prognosis of epilepsy were also surveyed. After a mean follow-up period of 18.9 years, we had sufficient data on 148 surviving patients aged 20-38 years (mean, 26. 0 years) and seven dead patients. The follow-up rate was 92.8%. In the overall group, the percentages of those who had had each of the following were as follows: (a) 5-year remission, 62.8%; (b) a relapse of seizures, 17.4%; (c) psychiatric complications, 2.7%; (d) mortality, 4.5%; (e) attendance at regular classes of an ordinary school during compulsory education, 71.6%; (f) entrance to high school, 65.5%; (g) employment, 67.4%; (h) marriage, 23.0%; and (i) acquisition of a driver's license, 54.7%. The educational and social variables of the control population were as follows: (e) 99.1, (f) 97.0, (g) 96.6, (h) 51.9, and (i) 94.8%. In the 99 patients of normal intelligence, the results of the same analysis were as follows: (a) 75.8, (b) 10.7, (c) 0, (d) 0.6, (e) 100, (f) 96.0, (g) 95.2, (h) 33.3, and (i) 77.8%, in contrast to the corresponding variables of the 49 patients with mental retardation, that is, (a) 36.7, (b) 44.4, (c) 8.2, (d) 12.2, (e) 14.3, (f) 6.1, (g) 20.4, (h) 2.0, and (i) 4.1%, respectively. The best predictors of seizure remission included an early response to therapy, a low frequency of seizures or an absence of status epilepticus prior to therapy, and normal mental development. As for the current awareness of epilepsy and its prognosis, nearly 40% of the patients did not know the true name of their illness, and the same proportion of parents were still anxious about the prognosis even if their children had been taken off medication. Our data show that the majority of patients with childhood-onset epilepsy have a favorable long-term medical prognosis in terms of seizure remission and psychiatric complications, whereas they have a higher mortality rate and lower levels of educational background as well as employment and marital status compared with the general population. However, except for the low marriage rate for the younger age group and the low rate of holding a driver's license, patients of normal intelligence appear to have more favorable long-term prognoses in terms of educational and social aspects as well. In Japan, individuals with epilepsy may not seek a driver's license because of the law.