In the differential diagnosis of the migraine headache syndromes, one should first consider the classification of headaches presented in Table 1. Headaches in general should be considered as a serious medical problem only when they become continuous or recur frequently, as almost everyone suffers from occasional headache. Although headache remains one of the most common medical complaints, even its most severe and chronic manifestations are rarely caused by organic disease. In a given year, nearly three quarters of Americans have headaches, but of these, only 5% seek medical help. When the complaint is of a persistent or recurrent headache, the history becomes of primary importance in establishing the proper diagnosis. The question arises as to which conditions are confused with migraine and when should one reasonably proceed to a more detailed investigation or referral to a specialist. In assessing the specific history of the headache, important facts to determine are onset, duration, periodicity, timing, localization, intensity, character, precipitating factors, accompanying symptoms and signs, and response to therapy. Often the exact description alone of the nature, duration, and timing of the headache permits the correct diagnosis. This is particularly true with migraine headache characterized by periodicity and associated symptoms.