Error, even if not made through negligence, always affects the physician. That probably explains why the literature on medical error is so sparse. Thanks to large surveys carried out mainly in American hospitals, awareness of the major role of this risk factor begins to appear. These studies demonstrate: three important facts: 1/ The frequency of errors with serious consequences is nearly 3% of all hospitalizations. 2/ Because of the growing complexity of modern health care system, medical errors have new characteristics. Even if they apparently originate from individual behaviour, they are in fact frequently rooted in the health care organisation and so are in fact systemic errors. 3/ A lot of these systemic errors could be prevented or corrected by measures at the level of the organisation. The study of mistakes is vital in implementing quality management of health care. Consequently it is the responsibility of the organisation to record and analyse adverse events. Each error can be an opportunity for safety improvement, provided it is acknowledged.