In this study, we test two explanations of why Protestants generally are more prone to suicide than Catholics. one theory stresses the importance of social support, while the other emphasizes the role of culture. A case-control study with 182 suicidal and 610 non-suicidal individuals was conducted. Denominational differences do not disappear after controlling for church attendance. Deeper involvement in the church community decreases suicide risk for Catholics, but increases it for Protestants. The relationship between education and suicide, while curvilinear for both religions, has a U-shaped form for Protestants, but an inverted U-shaped form for Catholics. Our findings corroborate the cultural explanation and demonstrate that the impact of integration on suicide can only be understood by taking cultural characteristics into account.