Background: The purpose of the present study was to examine the efficacy of cognitive- behavioural therapy (CBT) in a consecutive sample of patients suffering from drug-resistant obsessive-compulsive disorder (OCD) and to explore variables related to outcome. Method: Coadjuvant CBT was prescribed to 23 adult outpatients diagnosed with drug-resistant OCD (at least 2 different drugs had been prescribed). CBT had a maximum duration of 1 year, and was conducted in weekly, fortnightly, or monthly sessions. Subjects were assessed at baseline (T0), six months (T1), and twelve months (T2) by means of semi-structured interviews, Y-BOCS, CGI-Severity and CGIGlobal Improvement. Results: Four patients (17,4%) dropped out. The remaining 19 patients attended an average of 22,1 sessions. Large and significant (p=0,001) improvement of symptomathology (Y-BOCS) was observed in 73,9% of those who completed the process and 60,7% in the total sample (intent to treat analysis). Most of the improvement occurred during the first six months of treatment. 18 patients who completed the process responded to treatment: eight recovered completely, nine remitted and one had a full response. Level of insight, the amount of personal effort and being active (either through work or education) were associated with clinical response. Severity at onset and duration of OCD were associated with a worse outcome. Comorbidity with personality disorder showed a trend in the same direction. Conclusions: This study supports the usefulness of CBT in drug-resistant OCD. A number of potentially modifiable variables have a significant influence on outcome.