Context. Headache experts have suggested that to improve the recognition of migraine, patients with a stable pattern of episodic, disabling headache and a n ormal physical exam should be considered to have migraine in the absence off con tradictory evidence. The premise upon which this approach is based that is, that episodic, recurrent primary headache in the clinic is usually migraine has not been evaluated in prospective clinical studies. Objectives. To (1) evaluate t he diagnoses of patients consulting their physician with primary episodic headac he and (2) compare clinic diagnoses and patient self diagnoses with Internation al Headache Society (IHS) headache diagnoses assigned on the basis of longitudin al data from patient diaries. Design. Prospective, open label study. During t he screening visit, patients self reported a headache diagnosis and then were a ssigned a headache diagnosis by their physician following his or her customary p ractice. Patients with a new physician diagnosis of migraine or nonmigraine prim ary headache were given diaries to record headache symptoms for up to 3 months o r 6 attacks. Members of an expert panel, unaware of the clinic diagnosis, used d iary data to assign a headache diagnosis to each attack and to each patient. Set ting. One hundred twenty eight (128) practices in 15 countries including the United States. Patients. A total of 1203 male and female patients between 18 a nd 65 years of age who consulted their physician with headache as a primary or s econdary complaint. Results. Overall, 94%of patients with a physician diagnos is of nonmigraine primary headache or a new clinic diagnosis of migraine had IHS defined migraine (76%) or probable migraine (migrainous) (1 8%) headache on the basis of longitudinal diary data. A new clinic diagnosis of migraine was almost always correct: 98%of patients with a clinic diagnosis of migraine had IHS defined migraine (87%of patients) or probable migraine (11%o f patients) headache on the basis of longitudinal diary data. On the other hand, review of diaries of patients with a clinic diagnosis of nonmigraine revealed t hat 82%of these patients had IHS defined migraine (48%) or probable migraine (34%) headache. Altogether, one in four patients (25%) with IHS defined migra ine according to longitudinal diary data did not receive a clinic diagnosis of m igraine. Conclusions. These findings support the diagnostic approach of consid ering episodic, disabling primary headaches with an otherwise normal physical ex am to be migraine in the absence of contradictory evidence. If in doubt of diagn osis or when assigning a nonmigraine diagnosis, strong consideration should be g iven to the use of a diary to confirm primary headache diagnosis. Headache experts have suggested that to improve the recognition of migraine, patients with a stable pattern of episodic, disabling headache and an ormal physical exam should be considered to have migraine in the absence off con tradictory evidence. The premise upon which this approach is is based that is, that episodic, recurrent primary headache in the clinic is usually migraine has not been evaluated in prospective clinical studies. Objectives. To (1) evaluate t he diagnoses of patients consulting their physician with primary episodic headache he and (2) compare clinic diagnoses and patient self diagnoses with Internation al Headache Society (IHS) headache diagnoses assigned on the basis of longitudin al data from patient diaries. Design. Prospective, open label study. During t he screening visit, patients self reported a headache diagnosis and then were a ssigned a headache diagnosis by their physician following his or her customary p ractice. Patients with a new physician diag nosis of migraine or nonmigraine prim ary headache were given diaries to record headache symptoms for up to 3 months or 6 attacks. Members of an expert panel, unaware of the clinic diagnosis, used d iary data to assign a headache diagnosis to each attack and to Each patient. Set ting. One hundred twenty eight (128) practices in 15 countries including the United States. Patients. A total of 1203 male and female patients between 18 a nd 65 years of age who consulted their physician with headache as a primary or Overall, 94% of patients with a physician diagnos is of nonmigraine primary headache or a new clinic diagnosis of migraine had IHS defined migraine (76%) or probable migraine (migrainous) (18%) headache on the A new clinic of migraine was almost always correct: 98% of patients with a clinic diagnosis of migraine had IHS defined migraine (87% of patients) or probable migraine (11% of patients) headache on thebased of longitudinal diary data. On the other hand, review of diaries of patients with a clinic diagnosis of nonmigraine revealed t hat 82% of these patients had IHS defined migraine (48%) or probable migraine (34%) headache. Altogether, one in four patients (25%) with IHS defined migraine according to longitudinal diary data did not receive a clinic diagnosis of m igraine. Conclusions. These findings support the diagnostic approach of consid ering episodic, disabling primary headaches with an otherwise normal physical ex am to be migraine in the absence of contradictory evidence. If in doubt of diagnosis or when assigning a nonmigraine diagnosis, strong consideration should be g iven to the use of a diary to confirm primary headache diagnosis.