INTRODUCTION Assessing students is a key activity in health professional education programmes. It is tempting to simplify the process of assessment – we just want to know if our students have learned what we have taught them. How hard can that be? We give them a test. However, there are so many assessments to choose from, so many issues to consider when choosing and very little high-quality research evidence available to guide us. Where evidence is available, it oft en evaluates the qualities of a specifi c type of assessment but not whether it is the best choice for a particular assessment situation or desired outcome. Furthermore, much of the current evidence rests on expert opinion. However, as assessment is an important and required part of our curriculum, we need to evaluate the best available evidence and use it to make decisions about current practice and future research.