Objectives : The aims of this study were to assess a) the prevalence of trauma and posttraumatic stress disorder(PTSD) in schizophrenic patients and b) the differences in symptomatology and outcome after 1year treatment between those with and without PTSD. Methods : Twenty eight schizophrenia and schizoaffective disorder patients completed the Positive and Negative Syndrome Scale(PANSS), Life Stressor Checklist-Revised(LSCL-R), Clinician-Administered PTSD Scale(CAPS), Dissociative Experiences Scale(DES), Hamilton Psychiatry Rating Scale for Depression(HAM-D), and Rosenberg Self-Esteem Scale(RSE). Results : Twenty six patients(92.9%) had at least one trauma in their life time. Eleven patients(39.3%) were diagnosed with PTSD. PTSD group had significantly higher scores on HAM-D and DES but lower scores on RSE. PTSD group also had significantly lower score in the baseline PANSS Negative score. Higher CAPS scores were significantly correlated with lower baseline PANSS Negative score and greater change after 1year of PANSS Negative score. Conclusion : These results showed that the prevalences of trauma and PTSD are high in schizophrenic patients and suggested that PTSD and trauma-related symptoms affected the symptomatology and treatment outcome. More research is warranted to better understand the effects of PTSD in schizophrenic patients.