Background: IRT has been demonstrated as an effective treatment for severe, refractory OCD. Methods: Consecutive IRT subjects were ascertained over a 12 month period (female N = 26, male N = 35). Psychometric measures were completed at admission and discharge. from the McLean/MGH OCD Institute IRT, including the Yale-Brown Obsessive-Compulsive Scale (Y-BOCS), Beek Depression Inventory (BDI) and the Work and Social Adjustment Scale (WSA)(N = 61). These measures were repeated at one (N = 57), three (N = 42) and six months (N = 36) following discharge. This study was IRB approved. Results: OCD mean severity did not significantly worsen from discharge to the one (17.4, SD 6.5), three (116.5, SD 7.4) or six month (16.2, SD 7.3) follow-up (p > 0.25). Furthermore. the significant improvement from admission was maintained at each of the one (17.4, SD 6.5), three (16.5, SD 7.4) and six month (16.2, SD SD 7.3) follow-up time points (p < 0.001). Relapsers were significantly more likely to be living alone following discharge (p = 0.01), and were less likely to have comorbid illnesses (p = 0.02). There were no significant differences found between study dropouts and completers with regards to YBOCS scores (P > 0.47). Conclusion: In the first OCD IRT long-term follow-up study to date, findings have indicated that mean treatment gains were maintained at one, three, and six months post-discharge. This finding is important as it suggests that improvements of OCD severity were subsequently retained in home and work environments. Improvement of depression severity from admission was also maintained. (C) 2009 Elsevier Ltd. All rights reserved.