On August 30, 2010, the German Network for Health Services Research [Deutsches Netzwerk Versorgungsforschung e. V. (DNVF e. V.)] approved the Memorandum III "Methods for Health Services Research", supported by their member societies mentioned as authors and published in this Journal [Gesundheitswesen 2010; 72: 739-748]. Registries in Health Services Research vary in their aims and research questions as well as in their designs, methods of data collection, and statistical analyses. This paper aims to provide both a methodological guideline for developers to ensure a high quality of a planned registry and, to provide an instrument for users of data from registries to assess their overall quality. First, the paper provides a definition of registries and presents an overview of objectives in Health Services Research where registries can be useful. Second, several areas of methodological importance for the development of registries are presented. This includes the different phases of a registry (i. e., conceptual and preliminary design, implementation), technical organisation of a registry, statistical analysis, reporting of results, data protection, and ethical/legal aspects. From these areas, several criteria are deduced to allow the assessment of the quality of a registry. Finally, a checklist to assess a registry's quality is presented.