An internationally compatible medical thesaurus in German, the TdM, is presented. The principle of its structure is based on a documentation language including a complete hierarchic classification as well as a very variable faceted one. The structure items of the thesaurus are marked by abbreviations constructed mnemotechnically by letter corresponding to the hierarchic classification, the digits to the facet division. The organisation of the facets is done in such a way that they can be regarded as additional aspects within the arrangement of the hierarchic classification. The aspect of the meaning of a diagnosis is marked by a string, every item consisting of several strings. The number of strings is unlimited in general. The codification structures of the ICD/E, KDS and SNOP are included in every diagnosis. The thesaurus has a total volume of about 22,000 diagnoses.