BACKGROUND:Intensive residential treatment (IRT) is effective for severe, treatment-resistant obsessive-compulsive disorder (OCD). We sought to characterize predictors and course of response to IRT.METHODS:Admission, monthly, and discharge data were collected on individuals receiving IRT. We examined the association between baseline characteristics and percent change in OCD symptoms as measured by the Yale-Brown Obsessive-Compulsive Scale (Y-BOCS) using linear regression. We compared baseline characteristics of IRT responders (≥35% reduction in Y-BOCS) versus non-responders, and of patients who did versus those who did not achieve wellness (Y-BOCS ≤ 12) using non-parametric tests. To examine the course of OCD severity over time, we used linear mixed-effects models with randomly varying intercepts and slopes.RESULTS:We evaluated 281 individuals admitted to an IRT program. Greater baseline Y-BOCS scores were associated with a significantly greater percent reduction in Y-BOCS scores (β = -1.49 ([95% confidence interval: -2.06 to -0.93]; P < .001)). IRT responders showed significantly greater baseline Y-BOCS scores than non-responders (mean (SD) 28 (5.2) vs. 25.6 (5.8); P = .003) and lower past-year alcohol use scores than non-responders (1.4 (1.9) vs. 2.1 (2.2); P = .01). Participants who achieved wellness displayed lower hoarding factor scores than those who did not (5 (4.6) vs. 9.53 (6.3); P = .03). OCD symptoms declined rapidly over the first month but more slowly over the remaining two months.CONCLUSIONS:Higher baseline OCD severity, lower past-year alcohol use, and fewer hoarding symptoms predicted better response to IRT. IRT yielded an initial rapid reduction in OCD symptoms, followed by a slower decline after the first month.Copyright © 2014 Elsevier Ltd. All rights reserved.