QAHCS comprised a review of medical records of over 14,000 admissions in Australian hospitals in 1992, and estimation of the proportion of hospital separations associated with adverse events. For the purposes of the study, an adverse event was defined as an unintended injury or complication which results in disability, death or prolonged hospital stay, and is caused by health care management (rather than the patient's disease). Data on each adverse event identified in the review is contained in the database including information on the nature of the harm experienced by the patient and its consequences, and information on the circumstances in which the harm occurred.