- Background. Symptoms of post-traumatic stress disorder (PTSD) and depression are highly co-morbid following a traumatic event. Nevertheless, decisive evidence regarding the direction of the relationship between these clinical entities is missing. Method. The aim of the present study was to examine the nature of this relationship by comparing a synchronous change model (PTSD and depression are time synchronous, possibly stemming from a third common factor) with a demoralization model (i.e. PTSD symptoms causing depression) and a depressogenic model (i.e. depressive symptoms causing PTSD symptoms). Israeli adult victims of single-event traumas (n=156) were assessed on measures of PTSD and depression at 2, 4 and 12 weeks post-event. Results. A cross-lagged structural equation modeling (SEM) analysis provided results consistent with the synchronous change model and the depressogenic model. Conclusions. Depressive symptoms may play an important role in the development of post-traumatic symptoms.