Background: Many studies have been conducted to estimate the incidence and economic impact of adverse drug reactions. Most of these studies used historical data or were based on single hospital units. Little is known, however, about the frequency of serious adverse drug reactions in general practice.Objective: To estimate the incidence of serious adverse drug reactions in the community.Methods: A prospective study during 5 consecutive working days between March 1 and April 30, 1998, was conducted among a random representative sample of 254 general practitioners in Aquitaine, France. The main outcome measure was the number of serious adverse drug reactions (ie, resulting in death, life‐threatening condition, hospitalization, incapacity, or sequel) observed by each general practitioner during the study period and validated by an expert panel.Results: Thirteen validated serious adverse drug reactions, 2 of which were fatal (1 subarachnoidal hemorrhage with oral anticoagulant and 1 aplastic anemia with antineoplastics), were observed, resulting in an incidence density of 10.2 (95% confidence interval [CI], 5.4 to 17.5) per 1000 days of practice. Eleven case subjects (84.6%) were hospitalized. This represents an average of 2.6 cases per general practitioner per year, and 123,000 adverse drug reaction cases (95% CI, 65,400 to 210,000) for the 60,000 general practitioners in France. Antineoplastics and anticoagulants were the drugs most frequently involved, and blood dyscrasia and bleeding were the most frequent adverse drug reactions.Conclusion: This study, which is one of the few available that has prospectively measured the incidence of serious adverse drug reactions in general practice settings, confirms that serious adverse drug reactions are a major public health concern.Clinical Pharmacology & Therapeutics (2001) 69, 458–462; doi: 10.1067/mcp.2001.116145