The objective of this prospective study was to assess the efficacy and tolerability of duloxetine in the treatment of in military veterans with posttraumatic stress disorder (PTSD).Twenty subjects were enrolled in this 12-week, open-label trial. Diagnosis and symptom severity were assessed with the Clinician Administered PTSD Scale (CAPS). Depressive symptoms were assessed the Hamilton Depression Rating Scale. All subjects had a CAPS score of at least 60 at baseline. Subjects with lifetime history of psychotic disorders or bipolar illness were excluded. Fifteen participants completed 12 weeks of treatment, five dropped-out from the trial, 3 due to side effects. For patients who discontinued, missing values were estimated using "the last observation carried forward" method. Significant improvements were seen on: CAPS total and all subscales, depression and sleep measures. Most of the improvement was observed by week 2 of treatment. Nine participants (45%) were classified as responders, defined by 20% or greater improvement on CAPS total score. The mean daily dose of duloxetine was 81 mg. The most common side effects were constipation (20%) diarrhea (25%) and nausea (20%). Two subjects developed tachycardia, one withdrew from the trial due to this problem. Duloxetine had a fast onset of action and was effective in about half of the subjects, it was well tolerated in most subjects. These preliminary results in a difficult to treat population warrant the conduction of a double blind, placebo-controlled study of duloxetine in PTSD.