INTRODUCTION: There are two organised cancer screening programmes in Denmark, against cervical and breast cancers. The aim with this study was to give an overview of the available register-based research regarding these two programmes, to demonstrate the usefulness of data from the national registers. RESEARCH TOPICS: The register-based studies on cancer screening in Denmark could be grouped into research concerning effectiveness, in terms of mortality and incidence reduction, short-term indicators, e.g. in relation to recommended quality assurance indicators, and side effects, e.g. as false-positive results and overdiagnosis. CONCLUSION: The results indicate that registers have proven to be a valuable tool in evaluating the effects of ongoing screening activities. As they cannot be systematically used to test new screening technologies, register-based studies should not be seen as an alternative to randomised controlled trials, but as a supplement.