Exertional Heat Illness (EHI) is an important cause of significant illness during elite and mass-participation endurance sport. As the climate changes, EHI is becoming an increasingly important concern, resulting in otherwise healthy individuals requiring significant medical intervention and, in some cases, hospitalisation. The EHI Registry is prospectively collecting data from mass-participation sporting events across the UK. This talk will provide an update on data collection and early insights from the registry, as well as discussing the challenges associated with conducting this type of research.