The relevance of controlled vocabularies in promoting the standardized representation and exchange of clinical data is no longer to be proved. As part of a national project we evaluated the integration of classifications and terminologies in metadata registries based on the standard ISO/IEC 11179 Information technology - Metadata Registries (MDR). To overcome integration and maintenance tasks of monohierarchical classifications in the MDR, and to provide an exchange format between classifications publishers and the MDR, we implemented an import interface based on the Classification Markup Language (ClaML). The implementation transforms classifications from ClaML into a MDR conform structure using the Extensible Stylesheet Language Transformation (XSLT). Several XSLT-scripts were linked and successively executed. The national obliged classifications ICD-10-GM and OPS could be hence imported into the MDR. Problems arose with different interpretations and extensions of ClaML by WHO and the national publisher. We therefore advocate a unique interpretation of ClaML as prerequisite for a general use of the ClaML import interface.