The types, causes, contributing factors, and patient demographics of fatal medication errors were reviewed. Case reports of medication errors from hospitals, ambulatory care settings, and patients' homes that were entered in FDA's Adverse Event Reporting System during 1993-98 were the source of information on fatal medication errors. Each report was classified using predefined criteria and a taxonomy developed by the National Coordinating Council for Medication Error Reporting and Prevention. The types, causes, contributing factors, and patient demographics were identified, and the causality of each case was assessed to prevent future fatalities. The data indicated 5,366 medication error reports. Fifty-nine reports were excluded and classified as duplicate reports or intentional overdoses. Of the remaining medication error reports, 68.2% resulted in serious patient outcomes and 9.8% were fatal. Of the 469 fatal medication error reports, 48.6% occurred in patients over 60 years. The most common types of errors resulting in patient death involved administering an improper dose (40.9%), administering the wrong drug (16%), and using the wrong route of administration (9.5%). The most common causes of errors were performance and knowledge deficits (44%) and communication errors (15.8%). Fatal medication errors accounted for approximately 10% of medication errors reported to FDA and were most frequently the result of improper dosing of the intended drug and administration of an incorrect drug. A review of case reports of medication errors from 1993 to 1998 yielded information on the most frequent causes of and contributing factors involved in fatal medication errors.