Epidemiological cancer registries have now been established in all federal states of Germany. Though some are still in an initial phase and completeness has not yet generally been achieved, the use of the data for scientific purposes appears feasible. The examples presented in this paper demonstrate that scientific projects have already been conducted or are ongoing. However, the experiences also demonstrate that lack of completeness and partially the legal regulations on access to the data may hamper the use considerably. Efforts must now focus on (a) achieving completeness, e. g., by making the reporting system more efficient and (b) harmonizing the legal regulations on cancer registration among the federal states and fitting them to practice.