The influence of religious activity on the severity of religious delusions is unclear. This study examined whether Catholic and Protestant patients experienced more religious delusions than non-religiously affiliated patients. We also explored whether the severity of religious delusions, according to the Religious Delusions item on the Scale for the Assessment of Positive Symptoms (SAPS), was associated with the amount of religious activity. The Protestants experienced more religious delusions than Catholics and those without religious affiliation. Although when the groups were combined, patients who were more religiously active experienced more severe religious delusions (n=133), there was no difference in the severity of religious delusions across the non-religious, Catholic and Protestant groups. Religious affiliation may influence the frequency of religious delusions, particularly in Protestant individuals, but religious affiliation appears to be independent of religious delusion severity.