OBJECTIVES: Temperature observation time and type influenced the assessment of heat impact on mortality, and different health events may have different temperature thresholds beyond which these health events increase substantially. This study aimed to investigate whether temperature observation time and type influenced the assessment of heatwave impact on morbidity, to assess how heatwave duration modified heatwave impact on morbidity, and to examine whether there was a consistent temperature threshold beyond which five different types of health events increased sharply. METHODS: Minutely air temperature data in Brisbane, Australia, were collected and converted into five daily temperature indicators observed at different time points or calculated using different approaches. Twenty-nine heatwave definitions for each temperature indicator were used to examine the effects of heatwaves on five health events (i.e., ambulance service uses, emergency department attendances (EDAs), hospitalizations, possible EDAs of heat and/or dehydration, and possible hospitalizations of heat and/or dehydration) by quasi-Poisson models. RESULTS: Mean temperature was slightly better than maximum temperature in predicting heatwave impact on morbidity (P<0.05), and no appreciable difference in model performance was observed amongst different mean temperature indicators. Two-day-duration heatwaves were more detrimental than longer-lasting heatwaves when heatwave intensity was not high, and 97th percentile appeared to be a consistent temperature threshold for most heatwave-related health events (P<0.05). CONCLUSIONS: It seems desirable in the development of heatwave definition and early warning systems to use mean temperature as an exposure indicator, and to adopt the 97th percentile of temperature as the trigger in Brisbane. Health sectors need to better prepare for short-lasting heatwaves.