We examined the validity of the Personality Diagnostic Questionnaire--4+ (PDQ-4+) as a screening instrument for personality disorders among mentally ill prison inmates in Singapore. A total of 313 prison inmates completed the PDQ-4+ and the Structured Clinical Interview for DSM-IV Axis II Disorders (SCID-II). The subjects were 303 (96.8%) males and 10 (3.2%) females with a mean (SD) age of 40.7 (8.8) years. Kappa agreement between PDQ-4+ and SCID-II for the presence at least one personality disorder was moderate with high sensitivity and low specificity. For specific personality disorders and clusters, we found that the PDQ-4+ diagnosed more subjects as having each of the personality disorders than SCID-II with high negative predictive values. The area under the curve indicated moderate discriminatory capabilities. Our results suggest that the PDQ-4+ could be used as a potential screening instrument for personality disorders in prison inmates.