Religion plays a pivotal role in intergroup and interpersonal relationships in Northern Ireland, and individuals traditionally marry within their own religious group. However, 'mixed' marriages between Catholics and Protestants do occur and present an interesting, yet under researched, dynamic within this divided society. Both religion and committed relationships have been associated with physical and psychological health, but little is known about how divergence in religious beliefs within relationships impacts on health. A secondary data analysis of the Northern Ireland cohort of the Understanding Society: the UK Household Longitudinal Study was conducted to investigate the impact of mixed religion relationships on physical and psychological well-being in Northern Ireland. Less than 10 % of relationships were mixed religion relationships, and being in a mixed relationship was associated with poorer mental health but not with physical health. Mixed religion relationships in Northern Ireland are relatively uncommon in Northern Ireland, but are an important form of intergroup contact, as such it is important to fully understand the implications for the individuals involved and develop mechanisms to support those individuals psychological well-being.