A random cluster sample survey of approximately 18,000 people in 11 villages was performed in Ulanga, a Tanzanian district with a population of approximately 139,000 people. Well-instructed fourth-year medical students and neurologic and psychiatry nurses identified persons with epilepsy using a screening questionnaire and sent them to a neurologist for detailed evaluation. Identified were 207 subjects (88 male, 119 female) with epilepsy; of these, 185 (89.4%) (80 male, 105 female) had active epilepsy. The prevalence of active epilepsy was 10.2 in 1,000. Prevalence among villages varied, ranging from 5.1 to 37.1 in 1,000 (age-adjusted 5.8-37.0). In a 10-year period (1979-1988) 122 subjects living in the 11 villages developed epilepsy, with an annual incidence of 73.3 in 100,000. Generalized tonic-clonic seizures (GTCS) accounted for 58% and partial seizures accounted for 31.9%, whereas in 10.1% seizures were unclassifiable. Of the partial seizures, secondarily generalized seizures were the most common. Possible etiologic or associated factors were identifiable in only 25.3% of cases. Febrile convulsions were associated in 13.4 of cases. Other associated factors included unspecified encephalitis (4.7%), cerebral malaria (1.9%), birth injury (1.4%), and other (3%). In 38% of the cases, there was a positive family history of epilepsy.