The authors analyzed the nature of injuries sustained in a cohort of hospitalized patients in New York in 1984. Physician reviewers evaluated 1133 injury cases with respect to negligence, errors in management, and extent of disability. The reviewers found complications from medications were most common, followed by wound infections and technical complications. Nonsurgical events were more likely to be associated with negligence. The proportion of adverse events due to negligence was highest for diagnostic mishaps, errors of omission, and events in the emergency room, ranging from 70% to 77% in these categories. Errors in management were common as well; nearly half of these cases were attributed to negligence.