The rail, plane and ferry disasters during the final months of 1999 accompanied by many fatalities and injuries are tragic reminders of the risky nature of human endeavour (railway accidents in Paddington, London October; Sydney, Australia, December; aircraft accident Nantucket, New York, November; and ferry disaster Norway, November 1999). Such tragedies are examples of recurring worldwide but rare accidents in diverse industrial settings. They may have multiple causes involving many people at different levels within their respective organisations.1 Are accidents of this scale and impact a feature of the health care industry? The answer is yes. Recognition that such large scale accidents may occur is a fairly recent phenomenon, although their occurrence is not always obvious. Two important and substantive epidemiological studies indicate that the prevalence of iatrogenic harm (injury from care itself recorded as an adverse event) may range between 3.7% (the Harvard Medical Practice Study in the United States (US))2 to almost 16% (the Quality in Australian Health Care Study)3 in hospitalised patients. In the absence of data from other countries including the United Kingdom it may be assumed that similar rates apply to other Western health systems. However, it is unusual for a health care service to generate in a single time limited event large numbers of iatrogenically harmed hospitalised patients. Typically a number of patients may be affected over a longer time period but remain unrecognised for many months or years. The recent Bristol Royal Infirmary tragedy involving paediatric cardiac surgery is exemplar.4

Despite the lack of a simple explanation for such wide difference in rates between the two studies they are indicative of the enormous scale of iatrogenic harm in secondary care services. There is weak evidence of similar but perhaps less frequent occurrences in the primary and community services. …