The recent annual Hajj pilgrimage in Saudi Arabia in June, 2024, attracted a total of 1·83 million pilgrims, 1·6 million of whom were from 182 other countries. The Hajj was held during peak Saudi Arabian summertime when temperatures reached a record of 51°C, and 1301 pilgrim deaths due to heat-related illnesses were reported by the Saudi authorities. This unprecedented number of deaths has focused the attention of global public health authorities since the deaths occurred despite Saudi Arabia’s extensive range of carefully planned structural, operational, educational, and preventive measures, which have been developed over many years, to reduce the health risk of high ambient temperatures.