About 850 000 medical errors occur in NHS hospitals every year, resulting in 40 000 deaths.^w1In the United Kingdom, the National Patient Safety Agency (NPSA) was created to learn from patient safety incidents occurring in the NHS.^w2 In February 2004, it launched a new patient reporting system, drawing together reports of patient safety errors and systems failures provided by health professionals across England and Wales.^w3 An adverse event can be defined as “an unintended injury caused by medical management rather than a disease process, resulting in death, life threatening illness, disability at the time of discharge, admission to hospital, or prolongation of hospital stay.” ^w4 A medical or surgical misadventure is an adverse event that might have been avoided if the patient had received ordinary standards of care. We look at four years of …