In this large cross-sectional population-based study, 51,272 persons responded to a headache questionnaire and were screened for hemochromatosis. Phenotypic hemochromatosis and the C282Y/C282Y genotype were both associated with an 80% increase in headache prevalence evident only among women. The reason for this association is unclear, but one may speculate that iron overload alters the threshold for triggering a headache by disturbing neuronal function.