The need for effective surgical performance measurement has gained an increasingly high profile in recent years, particularly since events at Bristol Royal Infirmary, where apparent poor performance has prompted the UK Department of Health to instigate a major Public Inquiry. This paper describes issues that concern the measuring and monitoring of surgical performance, and methods that have been devised for judging a good surgeon from the less competent. The authors are a collaborative team composed of specialists in Cardiothoracic surgery and Operational Research analysts with experience of monitoring performance in cardiac surgery. This paper describes concrete examples from that knowledge base.