Objectives This study aims to examine the epidemiological characteristics of occupational heat illnesses in South Australia, to quantify the association between ambient temperature and occupational heat illnesses, and to investigate the impact of heatwaves on occupational heat illnesses.

Methods Workers’ compensation claims data and weather data were obtained from SafeWork South Australia and the Bureau of Meteorology, respectively, for 2001–2010. Time series analysis with generalised estimation equation models and linear spline functions was used to quantify the temperature–heat illness claims association. A case-crossover design was applied to investigate the impact of heatwaves on occupational heat illnesses.

Results There were 306 heat illness claims during the study period, with an incidence rate of 4.5 per 100 000 employees. The overall risk of occupational heat illness was positively associated with maximum temperature (T_max), especially when T_max was over the threshold of 35.5°C. One degree increase of T_max was associated with a 12.7% (incidence rate ratio 1.127, 95% CI 1.067 to 1.190) increase of occupational heat illness claims. During heatwave periods, the risk of occupational heat illness was about 4–7 times higher than that of non-heatwave periods.

Conclusions There is a need to develop or refine current heat-related regulations and guidelines to minimise the risk of occupational heat illnesses in vulnerable workers in a warming climate.