The role of religious orientation in group boundary maintenance was explored in the context of Fundamentalist Mormon polygamy. A sample of 2330 Protestants, Catholics, Mormons, Fundamentalist (polygamous) Mormons, and religious “nones” responded to a series of questions regarding sexuality, polygamy, religious orientation, religious doubt, and whether Mormons are considered Christian. Regression analyses indicate that attitudes regarding polygamy are predicted by attitudes toward alternative sexual practices for all groups except for Fundamentalist Mormons. Religious doubt, and considering Mormons to be Christian, were associated with relatively more favorable views toward polygamy. Intrinsic religious orientation was negatively correlated with polygamy attitudes, but this relationship reversed once conservative views toward sexuality were taken into account. The results are consistent with the view that alternative sexual and marital arrangements may generate differential treatment because of their implicit challenge to family structure.