Background: Posttraumatic stress disorder (PTSD) is a common and debilitating disorder among war vet-erans. Although complementary and altative therapies are gaining acceptance in the treatment of PTSD, the efficacy of animal-based therapies in this disorder is unknown. The goal of equine-assisted psy-chotherapy (EAP) is to improve the social, emotional, and/or cognitive functions of individuals with PTSD. Objective: This study aims to explore the effects of EAP on PTSD symptoms. We hypothesized that veter-ans with PTSD who participate in a standardized EAP program for 1 h per week for 6 weeks would expe-rience decreased PTSD symptoms and would demonstrate increased resilience as compared with individuals who do not receive EAP intervention. Design, setting, participants and interventions: We conducted a sequentially assigned, two-arm parallel group trial comparing 6 weeks of EAP with standard, previously established, ongoing PTSD therapy. Therapy was conducted at a community EAP facility in conjunction with an academic University Hospital. Twenty adult veterans with symptomatic PTSD completed the study. Ten adult veterans with previously diagnosed PTSD were assigned to EAP and received directed interaction with trained horses for one hour a week in groups of 3 or 4 individuals, while also continuing their previously established therapies. A certified therapist supervised the sessions, and a professional horse handler was also present. Results were compared with those from 10 adult veterans who only received their standard previously established PTSD care as prescribed by their provider. Main outcome measures: Changes in salivary cortisol, scores for the PTSD Check List-Military Version (PCL-M) and the Connor-Davidson Resilience Scale (CD-RISC) after 6 weeks of study were measured. Results: Of the 20 enrolled patients, 10 served in Afghanistan, 5 served in Iraq, and 3 served in Vietnam. Subjects were (47 ± 14) years old, were predominantly male, and had a body mass index of (29 ± 7) kg/m2. They had (9.2 ± 6.1) years of military service and carried 66％ ± 37％ service-connected dis-ability. PCL-M scores declined significantly in both groups and CD-RISC scores increased significantly in the EAP group. There was no difference between the groups with respect to the magnitude of change. Conclusion: As compared to the control group, a 6-week EAP program did not produce a statistically sig-nificant difference with respect to PCL-M and CD-RISC scores, or salivary cortisol. However, our results suggest that EAP may work as well as standard therapy with respect to these parameters. This study sup-ports further inquiry into EAP as a potentially efficacious altative for veterans suffering from PTSD.