Headache is pain localized to any part of the head, behind the eyes or ears, or in the upper neck. Headaches represent 2% of all emergency room visits. Ninety percent of men and 95% of women have at least one headache per year. Diagnostic clues should be derived primarily from history. Hallmark physical signs are often absent, and many physical findings are nonspecific. The majority of patients presenting with acute headache have a benign diagnosis, but a high index of suspicion should be maintained for life-threatening causes of headache.