Background: Obsessive-compulsive disorder (OCD) has been observed in a substantial proportion of patients with schizophrenia. Although cognitive-behavioural therapy (CBT) is well documented for OCD, few case studies are available regarding CBT for comorbid OCD in schizophrenia. Aims: The study aims to present a case study to augment the limited knowledge concerning CBT treatment for OCD in patients with schizophrenia. Method: The research adopted a case study approach, with a baseline condition and repeated assessments during the 3-week treatment and 6-month follow-up period. Results: The treatment was successful and the patient achieved clinical significant change in OCD symptoms. The patient had a reduction on the Y-BOCS from 24 to 5 (79%) and from 38 to 10 (73%) on the OCI-R from before treatment to 6 months follow-up. He did not fulfil the criteria for an OCD diagnosis at the end of the 3-week treatment period, or the follow-up at 3- and 6 months. Conclusions: The results strengthen the impressions given by previous case studies suggesting that CBT may be a promising treatment for OCD in patients with schizophrenia.