The aim of this study was to summarise the extent and characteristics of cases of illness due to environmental heat, significant enough to result in hospitalisation, and arising during sporting activity in Australia. Cases were identified from the hospital separations database compiled by the Australian Institute of Health and Welfare, using the allocated external cause and diagnosis codes and the activity code "While engaged in sports". Hospital separations for the 2 years 2002-2003 and 2003-2004 were used. One hundred and forty eight cases were identified (68% male). Cases were fairly evenly distributed across 10-year age groups starting from age 15 years, apart from fewer cases between 55 and 64 years. Nearly two thirds of the cases occurred in the summer months (December to February inclusive). The most commonly involved individual sports were lawn bowls, cricket, softball, golf, marathon running and walking, and the rate was highest for triathlons, lawn bowls, cricket, and running. Rates for persons aged 65 years or older were more than twice the rates at younger ages. Heat-related disorders are an uncommon cause of significant morbidity in Australians participating in sporting activity. However, particular sports have a relatively high rate of occurrence and these sports would provide an appropriate focus for prevention activity. The availability of a specific code in the International Classification of Diseases and Injuries to cover excessive endogenous production of heat would assist future analyses of the role of thermoregulatory disturbance in leading to morbidity in persons participating in sporting activity.