Patient safety was emphasized in anesthesiology long before other fields recognized its importance. This review of anesthesia incidents reported to the UK's National Patient Safety Agency categorizes the types of incidents and the level of harm associated with them. Many incidents could be attributed to human factors, as detailed in a prior classic study, and about one-quarter resulted in significant harm. Though limited by the voluntary nature of the error reporting system, this study provides a basis for examining systems associated with errors in anesthesia.