Headache can be caused by primary entities (as in migraine or tension-type headache) or the pain may result from secondary causes, such as brain tumors, idiopathic intracranial hypertension, chronic meningitis, hydrocephalus, drug intoxications, paranasal sinus disease, or acute febrile illnesses (eg, influenza). To determine the nature of a child's headache, the evaluation begins with a thorough medical history, followed by methodic physical examination with measurement of vital signs and complete neurologic examination. The diagnosis of primary headache disorders such as migraine and tension-type rests principally on clinical criteria as set forth by the International Headache Society (http://www.i-h-s.org/). Clues to the presence and identification of secondary causes of headache are uncovered through this systematic process of history and physical examination. The performance of ancillary diagnostic testing rests upon information or concerns revealed during the history and physical examination.