Posttraumatic stress disorder (PTSD) has been associated with hypothalamic–pituitary–adrenal (HPA) axis and immune function alterations; however, few studies have simultaneously investigated these systems in participants with PTSD. In this study, HPA axis and immune function in 26 women with PTSD with and without major depressive disorder was compared to 24 traumatized controls and to 21 nontraumatized controls. Posttraumatic stress disorder was associated with low cortisol and higher levels of DHEA and greater production of tumor necrosis factor‐α (TNF‐α) and interleukin‐6 (IL‐6) compared to traumatized and healthy controls. Women with PTSD and depression exhibited greater production of IL‐6 and higher levels of dehydroepiandrosterone (DHEA) than those with PTSD, but without depression. These findings suggest dysregulated HPA axis and immune function in women with PTSD, and that comorbid depression may contribute to these abnormalities.