The Comrades Marathon is South Africa's - and the world's - most recognised and largest ultra-marathon event, with over 15 000 par ticipants from across the globe competing in the 89-km road running event each year. Historically, the event has been held before the star t of austral winter (20 May - 17 June). However, in 2022, organisers of the race moved the event to 28 August, when austral spring commences. We explore the climate, in par ticular the Universal Thermal Comfor t Index (UTCI), of past Comrades events (1980-2019) and compare these data to UTCI data of the new proposed date (28 August) for the same period. The climatology for May, June, July and August was determined to identify periods with the lowest risk for 'strong' to 'very strong' heat stress. Results show that par ticipants' risk of exposure to 'strong' heat stress and 'very strong' heat stress periods will be more likely if the event is held in August as compared to the original event dates. Therefore, it is concluded that mid-June to mid-July has the lowest risk of heat stress exposure along the route. Runners and organisers should be aware of the higher risk of exer tional heat illness during the 2022 Comrades Marathon to ensure safe par ticipation.