A model of the clinical course of epilepsy from onset until remission or death has been developed for six prognostic groups, including survival, use and cost of medical care, and time lost from work and housekeeping. The model has been used to generate preliminary estimates of the lifetime cost of epilepsy for a cohort of persons diagnosed in 1990 in the United States. The distribution of incident cases among prognostic groups is derived from epidemiologic studies of prognosis in epilepsy. Direct cost is estimated by multiplying nationally representative unit costs by the expected type and frequency of medical care use. The latter were derived by an expert panel, based on inferences from existing literature and on their own clinical experiences. Indirect cost is estimated based on lost earnings associated with projections of restricted activity days, excess unemployment, and excess mortality. Total lifetime cost in 1990 dollars of all persons with epilepsy onset in 1990 was estimated at $3.0 billion, with indirect cost accounting for 62% of the total. Cost per patient ranged from $4,272 for persons with remission after initial diagnosis and treatment to $138,602 for persons with intractable and frequent seizures. Antiepileptic drug (AED) treatment is the most costly category of service. Different assumptions about the amount and type of drug administration cause major changes in overall cost estimates.