The study objective was to characterise human-biometeorological conditions in the summer season in the period 1966-2019 in Poland, with particular consideration of June 2019. The study was conducted based on data from the Institute of Meteorology and Water Management-National Research Institute (IMGW-PIB) for the years 1966-2019. The data provided the basis for the calculation of the Universal Thermal Climate Index (UTCI). The study revealed high spatial variability of human-biometeorological conditions in Poland, with strenuous character intensifying from the north to the south of the country. An increase in UTCI in the summer season was recorded in the studied multi-annual period. It was the most intensive in the north-eastern Poland. The consequence of the observed changes was an increase in the frequency of days with heat stress categories (days with UTCI > 26.0 degrees C), and a decrease in the frequency of days with cold stress categories (days with UTCI < 9.0 degrees C). Season 2019 stood out at the scale of the entire country in the context of the multi-annual period. This particularly concerns June, when mean monthly UTCI values were the highest in the analysed multi-annual period.