A database model for structure and access of theoretical medical knowledge is presented. The basic principle is the organization of knowledge in three dimensions: Each topic--first dimension--is explained with media--second dimension--in different versions of varying details--third dimension--suitable for different users. Every topic is one database entry. Topics are interconnected with heading and sub-topics (tree structure) and to logically related topics (cross references). Access follows the 3D-concept with initial access by topic, by media, or user specific, and with intra-unit access to related topics, media, and user specific versions. The model is discussed and possible implementations are described.