Headache is a common complaint in patients presenting to the emergency department. Most such headache are benign, but some have a more severe organic cause. Occasionally, patients present with a chronic headache disorder with which they can no longer cope. The new International Headache Society Classification of Headache is reviewed along with the differential diagnosis of benign headache disorders. Headache diagnosis by history is examined in detail followed by a discussion of the emergency presentation of headache patients. Causes for concern are presented, along with a detailed discussion of differential diagnosis, Including subarachnoid hemorrhage, meningitis, sinusitis, glaucoma, internal carotid artery dissection, and cerebro-vascular disease. Also discussed are medications used for the symptomatic treatment of headache, including analgesics, NSAIDs, narcotics, end ergotamine preparations. Approaches to the treatment of the severe, persistent headache in the emergency department are outlined and treatment options suggested. Headache medication overuse is discussed and guidelines are presented to recognize the condition and prevent its recurrence.