It has been suggested that the treatment strategy needs to be reviewed and changed if depression occurs in patients with posttraumatic stress disorder (PTSD). We analyzed data extracted from the Marmara Epidemiological Survey (MES) which had examined 683 survivors at 3 years after a devastating earthquake. Fifty three cases (40.5%) out of the 131 cases with PTSD had also been diagnosed with MDD. Comorbid PTSD and MDD group has significantly lower rates of recovery from PTSD in comparison to PTSD without MDD (26.4% vs. 47.4% respectively). Rates of past psychiatric disorder and past traumatic experience were significantly more frequent among the comorbid group. Moreover, comorbidity of PTSD and MDD was clearly associated with greater psychological distress, more severe PTSD, and diminished perceived social support. Past psychiatric disorder, General Health Questionnaire (GHQ-12) and Multidimensional Scale of Perceived Social Scale (MSPSS) total scores succeeded in predicting the comorbidity of PTSD and MDD significantly.