Men from a working population of black gold-miners were studied prospectively during an 8-month period to determine the incidence and aetiology of seizures in this population. Computed tomography (CT) of the brain was the primary investigation. From the total population of 97,000, 175 men with seizure disorders were admitted to the study and of these 165 underwent brain CT. In addition 138 subjects, who had brain CT for reasons other than seizures during the study period, served as controls. Sixty-three patients (38%) and 20 controls (14%) (P less than 0.0005) were considered to have definite or possible neurocysticercosis (NCC). Focal cerebral atrophy was the next most common abnormality and was found in 38 patients (23%) and 4 controls (3%) (P less than 0.0005). Otherwise unsuspected diagnoses, including tuberculoma, cerebral contusion and subdural haematoma, were made on CT in 10 cases. In 43% of patients with definite NCC, there was CT evidence of active disease and these subjects might be suitable candidates for treatment with antiparasitic chemotherapy. The high frequency of NCC in both the seizure patients and the control group indicates a need for more active public health measures. CT of the brain was extremely useful in determining seizure aetiology in this population.