Air temperature is one of major factors in a subjective assessment of human thermal comfort and discomfort. The work draws on a series of measurements of average daily air temperatures, relative air humidity and wind speed for 2000-2016 recorded at the Siedlce Meteorological Station. The station is part of the state observation and measurement network of the hydrological and meteorological service of The Institute of Meteorology and Water Management – National Research Institute (IMGW-PIB). Effective temperature was calculated according to the formula recommended by Missenard and thermal sensation was determined based on a scale suggested by Baranowska. There was calculated the number of days with individual thermal sensations in individual months of the long-term period, and months were put into groups of similar sensations by means of principal component analysis (PCA) and cluster analysis. In the last years (2015, 2014, 2012 and 2011) in months representing the cold season of the year, there were more days which were very cold and cold whereas the number of days with thermal comfort was much lower. The long-term period was split into three groups based on thermal comfort in the warm season of the year. The years which formed one group included 2011, 2013, 2015 and 2016 when there were no very cold days, the least cold days and the most very hot days.