Obsessive-compulsive disorder (OCD) is seen in many contrasting cultures but it is not known if the form of the disorder varies between these cultures. There have been anecdotal case reports where religion appeared to play a significant aetiological role in the disorder but the relationship between religion and OCD has not previously been systematically studied. This study was a retrospective, casenote study comparing the country of birth and religious affiliation of three groups of 50 patients. Its aim was to investigate the aetiological role played by religion in the development of OCD. The groups were patients with OCD from a specialist behavioural-cognitive unit, patients assessed in a specialist psycho-dynamic psychotherapy department and patients attending a general adult psychiatry outpatient department. More patients with OCD affiliated themselves with a religion as opposed to either of the other two groups. This difference disappeared when the type of religion was taken into account so that no conclusive relationship between OCD and religion could be identified. The findings do not diminish the importance of religion in the development of OCD in some individuals and suggest that future research in this area should include examination of the rigidity of upbringing and personal perception of the experience of strict rules or imposed religious practices.