This preliminary study examined the impact of aerobic exercise as an adjunctive intervention to regular care in reducing obsessive compulsive disorder (OCD) symptoms in a clinical sample. Fifteen patients (53% male; mean age = 44.4 years) receiving behavioral therapy and/or pharmacotherapy for OCD and who still demonstrated clinically significant OCD symptoms (i.e., Yale-Brown obsessive compulsive scale, Y-BOCS scores above 16) were enrolled in a 12-week moderate-intensity exercise intervention. Measures of OCD symptom severity were obtained at baseline, end of treatment, and at 3- and 6-week, and 6-month follow-up. Study findings at the end of this 12-week aerobic exercise intervention point to a beneficial effect (Cohen's d = 1.69) on reduction in OCD symptom severity. Further, reductions in OCD symptom severity appear to persist 6 months later. Lastly, improvement in overall sense of well-being was observed after the 12-week intervention. Results of this study suggest that a randomized clinical trial evaluating the efficacy of this 12-week aerobic exercise intervention is warranted.