Objectives: To study the efficacy, process, and related factors in trauma therapy among patients with psychiatric illness in general hospitals in Northeastern Thailand. Methods: This was a cross-sectional descriptive study that analyzed questionnaires and medical records on identification data, diagnosis, coping with adverse events, traumatic events, psychological symptoms, therapeutic process, and the results of psychiatric trauma therapy at Srinagarind and Khon Kaen Hospitals. Anxiety, depressive symptoms, and trauma-related symptoms were assessed pre- and posttreatment using the Hopkins Symptom Checklist [HSCL-25] and the Harvard Trauma Questionnaire. The data were analyzed for percentages, median, means, standard deviations, chi-square, t-test, and one-way ANOVAs. Results: There were 52 females and 12 males included. Complete assessments were done for 25 patients and the HSCL-25 and HTQ scores decreased significantly after the therapy. The respective number of eye movement desensitization and reprocessing [EMDR] sessions was significantly correlated with the baseline HSCL-25 and HTQ scores [i.e., Pearson correlation 0.49 and 0.44, p=0.012 and 0.028, respectively] and also correlated with overall improvement in HTQ scores and the cognitive symptoms subscale scores of HTQ [Pearson correlation 0.40 and 0.49, p=0.045 and 0.013, respectively]. Conclusion: Trauma therapy is effective in reducing anxiety, and depressive and trauma-related symptoms in psychiatric patients. The number of EMDR sessions is correlated with overall improvements in HTQ scores as well as the cognitive symptoms subscale scores of HTQ.