Scrupulosity is a form of obsessive compulsive disorder (OCD) characterized by a tendency to have persistent doubts about God, sin, and the adequacy of one's religious behaviors and devotion. To date, no published studies have compared scrupulosity in high- and low-religious Muslim and Christian samples. In the present study religious school students as well as high- and low-religious university students in Turkey and Canada were compared on the Penn Inventory of Scrupulosity (PIS), Obsessive Beliefs Questionnaire (OBQ-44), and symptom measures of obssesionality and negative affect. Between-group comparisons revealed that the highly religious Turkish sample scored significantly higher than the highly religious Canadian students on the PIOS Fear of God but not the Fear of Sin subscale. Separate multiple regression analyses revealed that the Clark-Beck Obsessive Compulsive Inventory (CBOCI) Obsessions subscale, OBQ-44 Importance and Control of Thoughts subscale, and guilt were significant unique predictors of PIOS scrupulosity. These findings suggest that subtle differences exist in how scrupulosity is manifested in Islamic and Christian believers.