The objective was to assess the prevalence of post-traumatic stress disorder (PTSD) in offenders who undergo forensic psychiatric evaluation (FPE), compare differences with regard to the prevalence of PTSD between immigrants and Swedes, compare psychiatric comorbidity and offenses between PTSD and non-PTSD patients, and compare various instruments and questionnaires when assessing the level of PTSD symptoms. Twenty-five immigrants and 25 Swedes were studied consecutively. The Clinician-Administered PTSD Scale (CAPS), Impact of Event Scale-22 (IES), Post-traumatic Symptom Scale (PTSS-10), and Structured Clinical Interview for DSM-IV (SCID)-PTSD were administered. In the immigrant group, 60 percent had PTSD, compared with 12 percent of the Swedes. Subjects with PTSD scored higher on IES-22 and PTSS-10 than those without PTSD. Considering the number of sexual and violent offenses together, the proportion of these types of offenses was higher in the PTSD group than in the non-PTSD group.