The role of genetic factors in determining risk for status epilepticus (SE) was examined in twins identified using the population-based Virginia Twin Registry. Concordance rates for SE were 0.38 for monozygotic (MZ) and 0.00 for dizygotic (DZ) twins, with the rate in MZs being significantly increased over DZs. The prevalence of SE in MZ co-twins of affected individuals was as high as 0.55. Clinical presentation of SE was evaluated, and no association was found between occurrence of SE and age at onset or seizure etiology. Genetic factors contribute to risk for SE.