Summary: The potential role of genetic factors in the etiology of posttraumatic and alcohol-associated seizures was studied in 289 male patients with recurrent seizures and in 174 individuals who had never experienced a seizure. The incidence of seizures in first-degree relatives of probands was compared with that in relatives of unaffected individuals. Relatives of patients with alcoholassociated seizures had a rate ratio of 2.45 [95% confidence interval (CI) 1.41–4.251, whereas no excess incidence was noted among relatives of posttraumatic epilepsy patients (rate ratio 1.20, 0.64–2.25 CI). Relatives of probands with both antecedents showed an intermediate rate ratio of 1.72 (0.92–3.20 CI). Among probands with alcohol-associated seizures, the rate ratio of 2.05 for patients with alcohol-related seizures (i.e., spontaneously occurring seizures in association with chronic alcohol abuse) was slightly higher than that of 1.85 for probands with alcohol withdrawal seizures. Trauma severity had a slight impact on the incidence of affected relatives; patients with severe head injuries had a rate ratio of 0.73 and probands with milder trauma had a rate ratio of 0.99. The results indicate a limited, if any, role of genetic predisposition in development of posttraumatic seizures. Alcoholrelated seizures, however, showed familial aggregation of unprovoked seizures, suggesting an involvement of genetic factors in the origin of such seizures.