The field of psychiatric medicine is observed to lag far behind physical medicine. The notion of how mental illness ought to be defined is still debated. This confusion reflects serious problems in the system by which mental disorders are classified. The utilitiy derived from the DSM-IV is, in some ways, undermined by the lack of scientific validity seen in the criteria employed therein. This paper suggests the use of a dimensional taxonomic model, onto which categorical criteria might be selectively superimposed. With such a system in place, a guide that expresses both utility for the clinician and va- lidity for the researcher might be found.