A monitoring system for cardiac surgery has been in use at Papworth Hospital for 10 years. We wished to determine whether this system would have detected an increase in deaths associated with a single practitioner, whether a poorly performing doctor or a serial killer such as Dr Harold Shipman, whose activites went undetected in the absence of a monitoring system for nearly a quarter of a century. Random extra deaths were artificially introduced into the practice of a surgeon and an anaesthetist in a way that broadly reproduced Shipman's pattern. The standard monitoring system was then used to analyse the hypothetical data thus generated. Using the current standard monitoring, the excess deaths would have been detected in less than 10 months. Suspicions would have been raised even earlier. Robust local quality monitoring of risk-adjusted outcomes is possible and, in our opinion, essential.