 Specific Aims: 1 To determine if there is evidence for the effectiveness and tolerability of adjunctive modafinil in the treatment of combat-related PTSD. We hypothesize that OEFOIF veterans with PTSD randomized to modafinil 100mgday for four weeks will experience more improvement in PTSD symptoms than OEFOIF veterans with PTSD randomized to placebo treatment for four weeks. 2 To determine if PTSD symptom severity is associated with electrophysiological and neuropsychological measures of pre-attention and attention and if these measures change to a greater degree in participants randomized to modafinil versus those randomized to placebo. We hypothesize modafinil treatment will result in greater changes in electrophysiological and neuropsychological measures of pre-attention and attention than placebo treatment. 