The association of fainting with specific situations and circumstances, such as the sight of blood, response to pain, prolonged standing position and fatigue, is well recognized and described in medical literature. Clinical experience also indicates that specific, local physical conditions, such as exposure to heat or remaining in a small, stuffy room may also trigger fainting. This paper verifies the hypothesis concerning the association between atmospheric conditions and the incidence of fainting. This is a retrospective cohort study of data relating to fainting collected in the city of Olsztyn (Poland). In total, 10,449 emergency service interventions in the period 2012-2019 that concluded with the R55 (syncope and collapse) diagnosis according to the ICD 10 were analyzed. The obtained data were matched with meteorological data, including basic parameters (temperature, humidity, atmospheric pressure) and complex parameters, with special attention given to the Universal Thermal Climate Index (UTCI). This index is derived from an analysis of human thermal balance and is particularly useful for describing the organism's response to thermal stress. Statistically significant differences in the occurrences of fainting depending on the season were revealed (more in the summer), but only for women. Among the analyzed meteorological and biometeorological parameters, statistical significance was found for parameters relating to temperature, with the greatest usefulness revealed for the UTCI. Periods with heat stress were more conducive to fainting, whereas the result for the general population was influenced by women in two age groups: 25-45 and 46-60. To our best knowledge, this is the first attempt worldwide to utilize the UTCI as a predictor of fainting. Our results confirmed the applicability of the UTCI as a universal biometeorological tool for the assessment of relationships between atmospheric conditions and the incidence of fainting.