Investigations of accidents in a number of hazardous domains suggest that a cluster of organisational pathologies-the "vulnerable system syndrome" (VSS)-render some systems more liable to adverse events. This syndrome has three interacting and self-perpetuating elements: blaming front line individuals, denying the existence of systemic error provoking weaknesses, and the blinkered pursuit of productive and financial indicators. VSS is present to some degree in all organisations, and the ability to recognise its symptoms is an essential skill in the progress towards improved patient safety. Two kinds of organisational learning are discussed: "single loop" learning that fuels and sustains VSS and "double loop" learning that is necessary to start breaking free from it.