Background: Posttraumatic stress disorder (PTSD) has been associated with neurocognitive deficits, such as impaired verbal memory and executive functioning. Less is known about executive function and the role of comorbid depression in PTSD. Recently, studies have shown that verbal memory impairments may be associated with comorbid depressive symptoms, but their role in executive function impairments is still unclear. Objective: To examine several domains of executive functioning in PTSD and the potentially mediating role of comorbid depressive symptoms in the relationship between executive function and PTSD. Method: Executive functioning was assessed in 28 PTSD patients and 28 matched trauma-exposed controls. The Cambridge Neuropsychological Test Automated Battery (CANTAB) with subtests measuring response inhibition (SST), flexibility/set shifting (IED), planning/working memory (OTS) and spatial working memory (SWM) was administered in PTSD patients and trauma-exposed controls. Regression analyses were used to assess the predictive factor of PTSD symptoms (CAPS) and depressive symptoms (HADS-D) in relation to executive function when taking into account the type of trauma. Pearson's correlations were used to examine the association between PTSD symptom clusters (CAPS) and executive function. The mediating effects of depression and PTSD were assessed using regression coefficients and the Sobel's test for mediation. Results: Our findings indicate that PTSD patients performed significantly worse on executive function than trauma-exposed controls in all domains assessed. PTSD symptoms contributed to executive functioning impairments (SST median correct, IED total errors, OTS latency to correct, SWM total errors and SWM strategy). Adding depressive symptoms to the model attenuated these effects. PTSD symptom clusters 'numbing' and to a lesser extent 'avoidance' were more frequently associated with worse executive function (i.e., IED total errors, OTS latency to correct and SWM total errors) than 'reexperiencing' and 'hyperarousal'. Depressive symptoms mediated the relation between PTSD and executive function on some executive function measures (IED total errors and OTS latency to correct), whereas PTSD did not mediate the relation between depression and executive function. Conclusions: PTSD patients perform worse on executive function. The impairments seem to be mostly associated with the less specific PTSD symptom cluster of 'numbing'. Depressive symptoms seem to mediate the relationship between PTSD and executive function. These findings may have clinical implications with regard to treatment indication and prognosis.