Living conditions, place of residence and surrounding natural as well as atmospheric environment determine human health status and life expectancy. This article presents the specificity of biothermal conditions as illustrated by the selected cities in Poland, with a particular consideration of unfavourable thermal conditions due to excessively high or low air temperature. The present article is a review. In accordance with the tendencies of climate change, it was found that in the cities in Poland, conditions hazardous to health and life due to excessively high temperature and heat stress as well as very strong heat stress, occur with increasing frequency, particularly in the city centre. Additionally, thermal discomfort which is markedly present in the city centre is aggravated and moved to night-time due to urban heat island. According to numerous studies, the incidence of such situations is less frequent in the coastal zone and in the suburban zones.