Introduction: Six in ten patients with obsessive-compulsive disorder (OCD) do not respond to the first-line treatments with serotonin reuptake inhibitor (SRI) or cognitive behavioural therapy including exposure and response prevention (CBT/ERP), and several do not respond to second-line treatments, i.e., SRI-second generation antipsychotic (SGA) or SRI-CBT/ERP augmentation. Evidence on third-line treatments is inconsistent. Objective: We investigated the 1-year response to SRI-CBT/ERP-SGA combination in patients with severe treatment-resistant OCD, who failed to respond to SRI and to SRI-SGA or SRI-CBT/ERP augmentation. Methods: Twenty-eight patients were consecutively recruited and treated with SRI (drug(s) and doses previously administere...