Severe accidental trauma often causes an immunosuppression accompanied by infection and sepsis which may be fatal. Furthermore, elective surgery could also cause dysfunction of the immune system. While physiopathological mechanisms of such posttraumatic immune system dysfunctions are still not sufficiently understood, the scope of research interest is focused particularly on the cytokine network and, recently, on the "nonspecific" mediators of oxidative stress. In this article some novel findings about the dysfunction of the immune system caused by trauma, including surgical injury, are briefly summarized, and the involvement of oxidative stress in these changes is emphasized.