To obtain accurate estimates of migraine prevalence, population-based studies are required. Clinic-based studies include a highly selected group of migraine sufferers. Even in population-based studies, there have been wide variations in estimates of migraine prevalence. A meta-analysis has shown that age, gender and case definition account for 70% of this variance. Recent studies using International Headache Society (IHS) diagnostic criteria have given relatively consistent estimates of migraine prevalence (about 15-18% of women and 6% of men) and indicate that migraine occurs most commonly in men and women aged 25-55 years. Migraine is a heterogeneous condition with a spectrum of severity and associated disability, and it is under-diagnosed worldwide.