The Magh Mela is the largest religious festival in the world and has a history spanning centuries with millions of pilgrims participating each year. Specifically, the study aimed to examine if, and if so, why, participation in a mass gatherings would lead to improvements in health. First, using a matched sample of participants (n=417) and non-participants (n=127), it was found that pilgrim's health improved significantly after having participated in the Magh Mela. Second, it was found that the increase in health could be explained by cognitive and behavioural crowd processes derived from Social Identity Theory (SIT; Tajfel & Turner, 1979; Turner, Hogg, Oakes, Reicher & Wetherell, 1985). The presentation will be concluded with findings from a smaller qualitative study that explored pilgrim's own attributions for their health changes as well a note on plans for future research in other parts of the world.