Climate change at the regional and local levels is forcing strong implementation of urban adaptation strategies related to climate-conscious urbanization and public health. Accordingly, the application of parameters that assess thermal stress in urban areas, such as outdoor thermal comfort (OTC) indices, is of paramount importance. As a contribution to this statement, long-term (1961-2020) datasets of daily OTC indices for the city of Banja Luka (Bosnia and Hercegovina) were used. Detailed temporal analysis using Physiologically Equivalent Temperature (PET), Universal Thermal Climate Index (UTCI), and Mean Radiant Temperature (Tmrt) was performed for (a) the entire research period, (b) the decadal level, and (c) defined heat/cold stress subcategories. The results show an intensive increase in extreme/strong heat days in the last 20 years, and the number of these days is five times higher than in the'70 s and'80 s. Decreasing tendencies are noticed in extreme/strong cold days towards the last two decades.