The aim was to estimate lifetime sex and age-specific incidence of migraine. Data are from the American Migraine Prevalence and Prevention study, a mailed survey sent to 120 000 US households. Age-specific incidence was estimated using self-reported data relevant to identification of migraine cases, age of onset of migraine and age at interview. Migraine incidence peaked between the ages of 20 and 24 years in women (18.2/1000 person-years) and the ages of 15 and 19 years in men (6.2/1000 person-years). Cumulative incidence was 43% in women and 18% in men. Median age of onset was 25 years among women and 24 years among men. Onset in 50% of cases occurred before age 25 and in 75% before age 35 years. Four of every 10 women and two of every 10 men will contract migraine in their lifetime, most before age 35 years. The incidence estimates from this analysis are consistent with those reported in previous longitudinal studies.