CONTEXT: In 1995, >5 million episodes of acute otitis media (AOM) accounted for $3 billion in health care expenditures. OBJECTIVES: To synthesize the literature on the natural history of AOM, the effectiveness of antibiotic treatment in uncomplicated AOM, and the relative effectiveness of specific antibiotic regimens. DATA SOURCES: Seven electronic databases for articles published between 1966 and March 1999 and reference lists in proceedings, published articles, reports, and guidelines. STUDY SELECTION: Two physicians independently assessed each article. Studies addressing AOM in children 4 weeks to 18 years old were included; those addressing children with immunodeficiencies or craniofacial abnormalities were excluded. Randomized, controlled trials (RCTs) were used to assess antibiotic effectiveness, and RCTs and cohort studies were used to assess the natural history of AOM. Among the 3491 citations identified, 80 (2.3%) met our inclusion criteria. DATA EXTRACTION: Two physicians independently abstracted data and assessed the quality of studies using a validated scale for RCTs and 8 quality components for cohort studies. DATA SYNTHESIS: Random-effects estimates of pooled absolute rate differences of outcomes were derived, and heterogeneity of both the rates and rate differences was assessed. Children with AOM not treated with antibiotics experienced a 1- to 7-day clinical failure rate of 19% (95% confidence interval: 0.10-0.28) and few suppurative complications. When patients were treated with amoxicillin, the 2- to 7-day clinical failure rate was reduced to 7%, a 12% (95% confidence interval: 0.04-0.20) reduction. Adverse effects, primarily gastrointestinal, were more common among children on cefixime than among those on ampicillin or amoxicillin. They were also more common among children on amoxicillin-clavulanate than among those on azithromycin. CONCLUSIONS: The majority of uncomplicated cases of AOM resolve spontaneously without apparent suppurative complications. Ampicillin or amoxicillin confers a limited therapeutic benefit. There is no evidence to support any particular antibiotic regimens as more effective at relieving symptoms. Certain antibiotics are more likely than others to cause diarrhea and other adverse events.