In a group of 299 migraine patients and 306 control subjects, the association of the -308 G/A polymorphism in the tumor necrosis factor-alpha gene (TNFalpha) with the occurrence and clinical characteristics of migraine was tested. Homozygosity for the G allele was associated with an increased risk of migraine (odds ratio [OR] = 2.85, p < 0.001). When the patients were divided into subgroups, the association was confirmed in patients affected by migraine without aura (OR = 3.30, p < 0.001) but not in migraine with aura. These data suggest that the TNFalpha gene or a linked locus significantly modulates the risk for migraine.