PURPOSE: To review the cause, pathophysiologic characteristics, cost, and treatment of alcohol-induced hangover. DATA SOURCES: A Medline search of all English-language reports (1966 to 1999) and a manual search of bibliographies of relevant papers. STUDY SELECTION: Related experimental, clinical, and basic research studies. DATA EXTRACTION: Data in relevant articles were reviewed, and relevant clinical information was extracted. DATA SYNTHESIS:The alcohol hangover is characterized by headache, tremulousness, nausea, diarrhea, and fatigue combined with decreased occupation, cognitive, or visual-spatial skill performance. In the United States, related absenteeism and poor job performance cost $148 billion annually (average annual cost per working adult, $2,000) Although hangover is associated with alcoholism, most of its cost is incurred by the light-to-moderate drinker. Patients with hangover may pose substantial risk to themselves and others despite having a normal blood alcohol level. Hangover may also be an independent risk factor for cardiac death. Symptoms of hangover seem to be caused by dehydration, hormonal alterations, dysregulated cytokine pathways, and toxic effects of alcohol. Physiologic characteristics include increased cardiac work with normal peripheral resistance, diffuse slowing on electroencephalography, and increased levels of antidiuretic hormone.Effective interventions include rehydration, prostaglandin inhibitors, and vitamin B6. Screening for hangover severity and frequency may help early detection of alcohol dependency and substantially improve quality of life. Receommended interventions include discussion of potential therapies and reminders of the possibility for congitive and visual-spatial impairment. No evidence suggests that alleviation of hangover symptoms leads to further alcohol consumption, and the discomfort caused by such symptoms may do so. Therefore, treatment seems warranted. CONCLUSIONS: Hangover, a common disorder, has substantial morbidity and societal cost. Appropriate management may relieve symptoms in many patients.