A small (N = 24) pilot study developed a new and brief cognitive-behavioural therapy (CBT) module for checking symptoms (CBT-C) in obsessive-compulsive disorder (OCD). CBT-C targets maladaptive beliefs about memory and results show that it is effective at significantly decreasing checking symptoms as compared to a waitlist control. The objectives of the current investigation are to further investigate CBT-C by (1) replicating the pilot results in a larger sample; (2) using an active control condition (treatment as usual) as the comparison condition (3) including a 6-month follow-up, and (4) determining whether the association between maladaptive beliefs about memory at pre-treatment assessment are related to degree of checking symptom reduction following CBT-C. The findings of the study will have theoretical significance in adding to our understanding of the maladaptive belief domains relevant to the development and maintenance of OCD and supporting the cognitive model of compulsive checking. The relevant clinical significance is the further development of an intervention that could improve outcomes in treatment of persons with OCD. The key practical outcome of the research would be to add a stepped care offering to patients with OCD.