BACKGROUND AND OBJECTIVES: The cognitive theory of compulsive checking in OCD proposes that checking behaviour is maintained by maladaptive beliefs, including those related to inflated responsibility and those related to reduced memory confidence. This study examined whether and when specific interventions (as part of a new cognitive therapy for compulsive checking) addressing these cognitive targets changed feelings of responsibility and memory confidence. METHODS: Participants were nine adults with a primary or secondary diagnosis of OCD who reported significant checking symptoms (at least one hour per day) on the Yale-Brown Obsessive-Compulsive Scale. A single-case multiple baseline design was used, after which participants received 12 sessions of cognitive therapy. From the start of the baseline period through to the 1 month post-treatment follow-up assessment session, participants completed daily monitoring of feelings of responsibility, memory confidence, and their time spent engaging in compulsive checking. RESULTS: Results revealed that feelings of responsibility significantly reduced and memory confidence significantly increased from baseline to immediately post-treatment, with very high effect sizes. Multilevel modelling revealed significant linear changes in feelings of responsibility (i.e., reductions over time) and memory confidence (i.e., increases over time) occurred following the sessions when these were addressed. Finally, we found that improvements in these over the course of the treatment significantly predicted reduced time spent checking. LIMITATIONS: The small sample size limits our ability to generalize our results. CONCLUSIONS: Results are discussed in terms of a focus on the timing of change in cognitive therapy