With the introduction of ICD-10 as the standard for diagnostics, it becomes necessary to develop an electronic representation of its complete content, inherent semantics and coding rules. Our design relates to the current efforts by the CEN/TC 251 to establish a European standard for hierarchical classification systems in healthcare. We have developed an electronic representation of ICD-10 with the eXtensible Markup Language (XML) that facilitates integration into current information systems and coding software, taking different languages and versions into account. In this context, XML provides a complete processing framework of related technologies and standard tools that helps develop inter-operable applications. XML provides semantic markup. It allows domain-specific definition of tags and hierarchical document structure. The idea of linking and thus combining information from different sources is a valuable feature of XML. In addition, XML topic maps are used to describe relationships between different sources, or semantically-associated parts of these sources. The issue of achieving a standardized medical vocabulary becomes more and more important with the stepwise implementation of diagnostically-related groups, for example. The aim of our work is to provide a transparent and open infrastructure that can be used to support clinical coding and to develop further software applications. We are assuming that a comprehensive representation of the content, structure, inherent semantics and layout of medical classification systems can be achieved through a document-oriented approach.