An analysis of 599 clinically definite multiple sclerosis (MS) patients including all known cases of the southern province of Finland in January 1, 1979 revealed epileptic seizures in 21 (3.5%) patients. On that date, 12 patients needed treatment (2.0%). The age-adjusted prevalence of active epilepsy was significantly higher than that in the general population. The percentage of partial seizures (67%) was significantly increased in proportion to a series of 100 adult epilepsy patients, with a comparable age distribution. In 10 patients (including three patients with symptomatic epilepsy), the attacks appeared before the MS symptoms. The mean follow-up after the first seizures was 19.3 years. In 10 patients, the seizures disappeared totally during the surveillance until September 1985. Our results show an increased comorbidity between MS and epilepsy. In most cases, however, the prognosis of epilepsy was good and there seemed not to be any clear correlation between the severity of MS and epilepsy.