Background: Recent factor-analytic studies in obsessive-compulsive disorder (OCD) identified consistent symptom dimensions. Support for the validity of these dimensions comes from studies of psychiatric comorbidity, functional brain imaging, genetic transmission, and treatment response to medications. This study examined whether previously identified OCD symptom dimensions are associated with treatment compliance and response to behaviour therapy (BT) for OCD. Methods: One hundred and fifty-three OCD outpatients who participated in a multi-centre randomised controlled trial of computer- versus clinician-guided BT for OCD were included in the study. Logistic and multiple regression models tested for significant predictors of compliance with and response to BT and relaxation. Results: The patients studied were phenomenologically comparable (including the presence of ‘pure’ obsessions and mental rituals) to those in previous serotonin reuptake inhibitor (SRI) trials and those in clinical epidemiology studies. High scorers on the ‘hoarding’ dimension were more likely to drop out prematurely from the study and tended to improve less. For those completing treatment, the strongest predictor of outcome was pre-treatment severity. Initial depression scores were unrelated to outcome. After controlling for symptom severity, higher scores on the ‘sexual/religious obsessions’ factor predicted poorer outcome with BT, especially when computer-guided. Conclusions: BT is especially indicated for OCD patients with aggressive/checking, contamination/cleaning and symmetry/ordering symptoms. Previous accounts of unsuccessful BT in patients with hoarding symptoms may be due in part to their propensity to drop out earlier from treatment. Patients with sexual/religious obsessions, but not those with mental rituals, might respond less well to traditional BT techniques. Existing treatments need to be refined and/or new treatments developed to improve these patients’ adherence and response to treatment.

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While the results of this meta-analysis support the superiority of clomipramine, head-to-head, double-blind comparisons of these compounds would be the best test of comparative efficacy and tolerability.