We investigated comorbidity of migraine and epilepsy by using information from structured telephone interviews with 1,948 adult probands with epilepsy and 1,411 of their parents and siblings. Epilepsy was defined as a lifetime history of two or more unprovoked seizures, and migraine as severe headaches with two or more of the following symptoms: unilateral pain, throbbing pain, visual aura, or nausea. Cumulative incidence of migraine to age 40 was 24% in probands with epilepsy, 23% in relatives with epilepsy, and 12% in relatives without epilepsy. Using Cox proportional hazards analysis to control for years at risk and gender, the rate ratio for migraine was 2.4 (95% CI, 2.02 to 2.89) among probands and 2.4 (1.58 to 3.79) among relatives with epilepsy in comparison with relatives without epilepsy. Migraine risk was highest in probands with epilepsy due to head trauma, but it was significantly higher in every subgroup of probands than in unaffected relatives when probands were stratified by seizure type, age at onset, etiology of epilepsy, and history of epilepsy in first-degree relatives. Age-specific incidence of migraine among probands was increased to a greater extent after onset of epilepsy than before, but it was also significantly increased more than 5 years before onset and 1 to 5 years before onset. These results indicate that migraine and epilepsy are strongly associated, independent of seizure type, etiology, age at onset, or family history of epilepsy.