We present validation of a simple questionnaire designed to screen the general population for migraine. It comprises four questions: (1) "Have you ever had migraine?" (2) "Have you ever had severe headache accompanied by nausea?" (3) "Have you ever had severe headache accompanied by hypersensitivity to sound and light?" (4) "Have you ever had visual disturbances lasting 5-60 min followed by headache?" A telephone interview carried out by a physician was used as an index of validity. The study population was 5,360 twins from the population-based Danish Twin Registry. All twin pairs where at least one twin had answered "yes" to at least one of our questions were eligible for the telephone interview (n=2,272 twins). The response rate to the questionnaire was 87%; the participation rate in the telephone interview was 90%. The questionnaire ascertained 85% of all migraineurs (sensitivity). A combination of two questions (questions 1 and 4) extracted 93% of the twins with migraine with aura and 74% of the twins with migraine without aura, yet only 26% of the sample needed to be interviewed. We conclude that in the Danish population two simple questions are sufficient to screen for migraine in selecting participants for a diagnostic clinical interview. Our questionnaire clearly merits further study to document its universal applicability.