Voluntary physician reporting of adverse drug events (ADEs) in their patients remains the single most important source of information on serious and rare ADEs. Yet, substantial underreporting exists and the factors producing it are unclear. We surveyed 3000 randomly chosen physicians by mailed questionnaire to determine their knowledge about the reporting system, attitudes toward reporting, and their past behavior in reporting the ADEs they had detected. Responses numbered 1121. Only 57% were aware of the Food and Drug Administration's reporting system. While 418 physicians had detected an ADE in their practices during the previous year, only 21 physicians reported these events directly to the Food and Drug Administration. The physicians appear to appreciate the safety issues involved in prescription drug use and view reporting as a professional obligation; however, the current reporting system is considered inconvenient.