1. Two types of psychiatric diagnoses were obtained in a study of the course of early dyskinesia: DSM-III-R and Dimensional Global Ratings of Schizophrenia, Paranoia, Mania and Depression. 2. The strength of association between measures of vulnerability to developing tardive dyskinesia (TD), and clinical components from each of the two methods of obtaining psychiatric diagnoses was established by canonical correlations. 3. Overall, little difference was obtained between DSM-III-R categories and Global Ratings in terms of correlations with TD vulnerability measures. Using components from global diagnostic ratings, the Depression and Schizophrenia Scales made stronger contributions to the canonical functions than Mania and Paranoia. 4. Unipolar depressed patients appear more sensitive to NL: they developed TD after less NL exposure. 5. Dimensional classification appears to be a promising approach to capturing important characteristics of psychoses.