Henrik Toft Sørensen, Timothy L LashDepartment of Clinical Epidemiology, Aarhus University Hospital, DK-8000 Aarhus, DenmarkFor many decades, cancer registries have been a cornerstone in monitoring cancer occurrence in different populations. Cancer registries in the Nordic countries are characterized by a high level of completeness and excellent data quality.1 Cancer diagnoses are often validated through several procedures, with documentation of clinical evidence for the diagnosis. Cancer registries have proven very useful in monitoring cancer incidence, contributing significantly to our understanding of its origin and development. Some registries also have been used to monitor cancer survival at the population level.1