To identify the optimum combination of symptoms for the International Headache Society (IHS) diagnostic criteria for migraine, the criteria were systematically assessed for validity using an epidemiologic sample from Zurich, Switzerland. The indicators of validity used included subjective distress, occupational impairment, family history of migraine, and treatment. The symptoms that provided the best discrimination between migraine and other headache subtypes were photophobia, phonophobia, and osmophobia, in combination with gastrointestinal symptoms. The evaluation of the validity of the IHS classification of migraine is impeded by several factors, including: the presence of multiple headache syndromes within an individual, the tendency for headache characteristics to change over a lifetime, the effects of headache treatments in obscuring syndromes, and the lack of generalizability of findings based on clinical samples. The methods used in this study serve as a model for applying statistical techniques for evaluating the validity of diagnostic criteria. The findings, however, should be replicated in additional studies to determine their generalizability to specific demographic and clinical subgroups.