This study is designed to test the hypothesis that events like the Holly Bough service held in Liverpool Cathedral on the fourth Sunday of Advent that attracts a wide range of participants, including regular churchgoers and occasional (sometimes annual) visitors, contribute significantly to the psychological health and well-being of these participants. At the Holly Bough service held in 2019, a total of 383 participants (139 men, 229 women and 15 individuals who preferred anonymity) completed a recognised measure of psychological health (...) and well-being (the Oxford Happiness Questionnaire) whilst they were waiting for the service to begin and again during a 5-min organ improvisation just before the close of the service. The data demonstrated a significantly higher score on the Oxford Happiness Questionnaire at time 2 than at time 1, suggesting that the experience of the service functioned as an agent of psychological health and well-being. Contribution: Situated within the science of cathedral studies, this paper confirms by means of a repeated-measure study that cathedrals promote psychological health; 383 participants at a Christmas service completed the same well-being measure before and after the service, with a significant increase in scores at time two. (shrink)