OBJECTIVE: To evaluate whether an antimicrobial review system is associated with a reduction in antimicrobial-associated adverse events. DESIGN: All antimicrobial medication orders for patients hospitalized over a two-year period were evaluated. High-level interventions intended to prevent adverse antimicrobial events were collated. Based on literature estimates of adverse antimicrobial events, potential reduction of high-level adverse antimicrobial events was estimated. SETTING: Department of Clinical Pharmacy and Division of Infectious Diseases at a tertiary care teaching hospital. RESULTS: A total of 452 interventions were classified as "high-level." The incidence of preventable adverse antimicrobial events requiring intervention was 16 per 1000 antimicrobial orders. The incidence of high-level errors necessitating intervention was 4.4 per 1000 antimicrobial orders. An estimated 125 to 198 high-level adverse events were avoided. CONCLUSION: An antimicrobial review program has the potential to reduce significant adverse events in hospitalized patients.