This study examines bioclimatic conditions in Vilnius, Lithuania, from 1993 to 2024, using the Universal Thermal Climate Index (UTCI) to analyze trends in human thermal stress. RayMan software was employed to calculate UTCI data based on input parameters such as average air temperature, relative humidity, wind speed, and cloud cover. The Mann-Kendall trend test was applied to identify statistically significant changes in thermal stress over time. The second part of this research compares data from three different meteorological stations (located outside the city, north of the city centre, and within the city centre), focusing on extreme heat stress conditions from 2022 to 2024. Results show an increase in moderate and higher heat stress events, along with a decrease in strong and lower cold stress events. The variation in UTCI category frequencies over the years demonstrates a shift toward higher thermal stress levels and more instances of no thermal stress. A comparison of data from the three stations reveals that extreme heat stress conditions are more common in the city centre than in the northern part and outskirts of the city. These findings have implications for public health, urban planning, and climate adaptation strategies in Vilnius, highlighting the city’s growing need for heat mitigation measures.