Regional comparison of cancer incidence rates is one of the most important and most challenging tasks in cancer epidemiology. If the degree of completeness of case ascertainment differs between the regions compared - which it usually does - no meaningful comparison is possible. Therefore, completeness has to be assessed and differences adjusted before regional comparisons can be conducted. In this book, five internationally recommended methods for completeness estimation in cancer registries, suitable for routine use, have been evaluated. For the first time completeness of the Austrian National Cancer Registry has been assessed on national and regional level. The findings show ways to increase quality of cancer registries.