Through the use of IHS criteria, large population-based epidemiologic studies in Denmark, the United States, France, Canada, and elsewhere have shed light on the descriptive epidemiology of migraine. Although migraine is a remarkably common cause of temporary disability, many migraineurs, even those with disabling headache, have never consulted a physician for the problem. Prevalence is highest in women, in persons between the ages of 25 and 55, and, at least in the United States, in individuals from low income households. Nonetheless, it occurs with high prevalence outside these groups at highest risk. The prevalence of migraine may be increasing in the United States, but this is uncertain. Longitudinal studies are required to better determine the incidence and natural history of migraine, as well as the life course of comorbid conditions.