The Posttraumatic Diagnostic Scale (PDS) is a brief, self-report questionnaire developed for the diagnostic screening and assessment of the severity of posttraumatic stress disorder (PTSD); the PDS is based on the criteria outlined in the Diagnostic and Statistical Manual of Mental Disorders (4th edition; DSM-IV). We investigated the validity and reliability of the Japanese version of the PDS in a clinical (n=109) and a non-clinical (n=116) sample, recruited from an outpatient psychiatric facility and a university student population, respectively. The Japanese versions of the PDS and the Clinician-Administered PTSD Scale (CAPS/DSM-IV) were administered to the participants. The Japanese PDS's diagnostic sensitivity and specificity exceeded 90%. The correlation between the severity scores assessed by the Japanese PDS and the CAPS was also high (r=0.92). The findings suggest that the Japanese version of the PDS is useful for diagnostically screening PTSD and assessing symptom severity.