Global wanning has led to renewed interest in the occurrence of heat stress in the population along with its determinants and consequences. Heat stress can create unsafe working conditions and affect the health of workers. Heat waves are also unsafe and in 2003 led to many avoidable deaths in Europe. Most heat stress research has been conducted in high-income countries in temperate latitudes. This leaves knowledge gaps regarding heat stress and its effects for tropi cal settings. Thailand is a tropical developing country where average temperatures have increased over the last 50 years and further increase is expected . Heat stress has been shown to be a serious problem in a variety of Thai workplaces. But several impo1iant public health questions remain and they are the focus of this thesis. The questions are as follows: are there any health impacts of heat stress i) on Thai workers? ii) on the overall population in Thailand? iii) expected for the Thai popul ation in future due to the projected increase of temperature? To answer these research questions, five studies were carried out. They investigate the occurrence of heat stress and its association with various health outcomes, including death. The first four studies use heat exposure and morbidity data from a large national Thai Cohort Study (TCS) covering the period 2005 to 2009. The fifth stud y uses national weather and mortality data covering 1999 to 2008.Global wanning has led to renewed interest in the occurrence of heat stress in the population along with its determinants and consequences. Heat stress can create unsafe working conditions and affect the health of workers. Heat waves are also unsafe and in 2003 led to many avoidable deaths in Europe. Most heat stress research has been conducted in high-income countries in temperate latitudes. This leaves knowledge gaps regarding heat stress and its effects for tropi cal settings. Thailand is a tropical developing country where average temperatures have increased over the last 50 years and further increase is expected . Heat stress has been shown to be a serious problem in a variety of Thai workplaces. But several impo1iant public health questions remain and they are the focus of this thesis. The questions are as follows: are there any health impacts of heat stress i) on Thai workers? ii) on the overall population in Thailand? iii) expected for the Thai popul ation in future due to the projected increase of temperature? To answer these research questions, five studies were carried out. They investigate the occurrence of heat stress and its association with various health outcomes, including death. The first four studies use heat exposure and morbidity data from a large national Thai Cohort Study (TCS) covering the period 2005 to 2009. The fifth stud y uses national weather and mortality data covering 1999 to 2008.