Background: Cognitive behavioural interventions for excessive reassurance seeking (ERS) typically focus on encouraging individuals to refrain from seeking any reassurance and in some cases banning caregivers (e.g. family members) from providing it. However, this blanket consideration that reassurance is a bad thing that should simply be stopped may not always be appropriate or helpful. Cognitive behavioural treatment (CBT) targeting ERS by helping the sufferer to shift from seeking reassurance to seeking support may be a promising treatment intervention. Aims: This study aims to examine the targeted treatment of ERS in an older adult who has been suffering from severe obsessive compulsive disorder (OCD) for seven decades. Method: Using a single case quasi-experimental design (ABCD), the frequency of reassurance seeking, urges to seek reassurance, OCD beliefs and anxiety were measured daily for almost a year in addition to standard symptom measures. Results: At the end of treatment, visual inspection showed that reassurance seeking was no longer considered excessive and OCD severity fell from the severe to non-clinical range across the treatment sessions. All treatment gains were maintained at follow-up. Conclusions: This study illustrates how CBT can be successfully applied to treat long-standing OCD and ERS in an older adult. Engendering support as an alternative to reassurance seeking in CBT may be a particularly promising intervention for ERS.