Aims and method To establish whether cognitive-behavioural therapy (CBT) with response and exposure prevention (ERP) is effective in individuals with obsessive-compulsive disorder (OCD). Twenty-four patients with OCD, divided into four groups, participated in ten sessions of group CBT. All patients completed the Yale-Brown Obsessive-Compulsive Scale (Y-BOCS), the Maudsley Obsessive-Compulsive Inventory (MOCI), the Beck Depression Inventory (BDI) and the Beck Anxiety Inventory (BAI) pre- and post-treatment. Results The mean (s.d.) YBOC score post-treatment was 17.1 (5.8). This was significantly lower than the mean (s.d.) YBOC pre- treatment (24.7 (6.1); t = 8.4, d.f. = 23, P<0.005). A significant reduction was also observed in relation to all other rating scales. Clinical implications Cognitive-behavioural therapy for OCD delivered in a group setting is a clinically effective and acceptable treatment for patients. The use of group-based CBT is an effective means to improve access to psychotherapy.