OBJECTIVE Post Traumatic Stress Disorder (PTSD) is known to be associated with Erectile Dysfunction (ED). Sildenafil citrate was shown to be effective treatment for ED among different clinical populations. However, to date, no placebo-controlled trial has assessed sildenafil's effectiveness for treating ED in PTSD patients. The goal of the present study was to address this question using a double-blind placebo controlled crossover design. METHODS A four-week double-blind crossover trial of sildenafil (50 mg up to 100 mg per usage) versus placebo was conducted on 21 outpatients diagnosed with chronic PTSD accompanied by ED. Erectile function was assessed biweekly using the International Inventory of Erectile Function (IIEF). Depressive symptoms, PTSD symptoms and subjective well-being scores were assessed as well. RESULTS Analysis of IIEF scores revealed a main effect of treatment phase (E = 33.361, df =2, P < 0.000). Pairwise comparisons showed that sildenafil IIEF scores (mean = 45.19 +/- 15.05) were significantly higher compared to baseline scores (mean = 20.00 +/- 12.32, P = 0.000) and placebo scores (mean = 33.04 +/- 12.99). Compared to placebo, a significant improvement was also observed during the sildenafil phase in erectile function, orgasmic function and sexual desire. There was no significant change in depression, PTSD symptoms or subjective well-being. CONCLUSION The results of this study suggest that sildenafil citrate treatment for ED in PTSD patients was accompanied with improvement of ED symptoms and was found to be significantly better than placebo. Nevertheless, this effect should be considered marginal since patients still meet the criteria of ED after treatment. Larger, parallel group studies are warranted.