A modified version of the revised Personality Diagnostic Questionnaire (PDQ-R), based on DSM-III-R personality disorders (PD), was completed by 74 psychiatric patients. A factor analysis of the scores for each of the PD (i.e. of the number of positive DSM-III-R criteria for each of the PD) yielded 3 factors that defined 3 PD clusters. These were similar to the 3 DSM-III-R PD clusters for 7 of the 11 PD categories. The 3-group solution of a cluster analysis of the patients (using their scores of positive criteria for each of the PD) did not reflect these factors; the main discriminating variable between the 3 groups of patients was the total number of positive PD criteria. It is suggested that, for the routine assessment of patients, the most important derivative of the DSM-III-R classification of PD is the total score of positive PD criteria.