We have examined data from 107 motor-vehicle accident (MVA) victims with regard to whether the presence of comorbid depression is important clinically, and with regard to whether the threshold for diagnosing the comorbid depression should be raised because of symptom overlap between posttraumatic stress disorder (PTSD) and major depression. Of the 62 MVA victims who met the criteria for PTSD 1 to 4 months post-MVA, 33 also met the criteria for major depression, with 27 cases for which the depression occurred post-MVA. A LISREL 8.12a analysis indicates that PTSD and major depression are correlated, but independent, responses to trauma. Those with PTSD and depression are more subjectively distressed, suffer more major role impairment, and remit less readily over the first 6 months of prospective follow-up than those with PTSD alone. The threshold for diagnosing comorbid depression (5 or 6 depressive symptoms versus 7 to 9 depressive symptoms) has no important effects on any of the indicators of "caseness."