A key point that the UK General Medical Council addressed in its recommendations on the undergraduate medical education was the concept of 'core curriculum' (General Medical Council 1993). Although enthusiastic for the idea of reducing factual overload, many medical teachers found themselves facing the task of how to define what a core curriculum is, what should be included and why. Predictably, our initial response is to include common and important topics, but how common is common, and how does one determine the relative importance of topics? We do not claim to have unravelled all the ambiguities surrounding the subject nor to have resolved all the controversies that are inevitably encountered. We hope, however, to describe some of the principles that governed our approach and put forward some guidelines, that may contribute to the debate.