The most common cause of heat fatalities is environmental exposure during heat waves. Deserts of the southwestern USA are known for temperatures that exceed 32 degrees C for 30 days or more; yet, heat-related fatalities are rare among residents of the region. We compiled data from the National Weather Service and the Office of the Medical Examiner in order to determine the relationship between temperature and occurrence of heat fatalities in Pima County, AZ. Logistic regression indicated that for each degree of increase in temperature (degrees C), there was a 35% increase in the odds of a heat fatality occurring (p<0.001).