We tested the efficacy of the Equine Partnering Naturally(©) approach to equine-assisted therapy for treating anxiety and posttraumatic stress disorder (PTSD) symptoms. Participants were 16 volunteers who had experienced a Criterion A traumatic event, such as a rape or serious accident, and had current PTSD symptoms above 31 on the PTSD Checklist (PCL-S; Weathers, Litz, Herman, Huska, & Keane, ). Participants engaged in tasks with horses for 6 weekly 2-hour sessions. Immediately following the final session, participants reported significantly reduced posttraumatic stress symptoms, d = 1.21, less severe emotional responses to trauma, d = 0.60, less generalized anxiety, d = 1.01, and fewer symptoms of depression, d = 0.54. As well, participants significantly increased mindfulness strategies, d = 1.28, and decreased alcohol use, d = 0.58. There was no significant effect of the treatment on physical health, proactive coping, self-efficacy, social support, or life satisfaction. Thus, we found evidence that the Equine Partnering Naturally(©) approach to equine-assisted therapy may be an effective treatment for anxiety and posttraumatic stress symptoms. Future research should include larger groups, random assignment, and longer term follow-up.