Medical Informatics needs a specific terminology that reflects the multi-disciplinary nature of the field and can rapidly change as the discipline evolves. Using the four primary methods of thesaurus construction, a group at the University of Missouri-Columbia is developing a thesaurus that meets these criteria and includes both user and literary warrant. The steps in construction include using existing thesauri, medical informatics literature, and the terminology of experts to produce a thesaurus arranged within a hierarchical structure.