Abstract Several complex thermal indices (e.g. Predicted Mean Vote and Physiological Equivalent Temperature) were developed in the last decades to describe and quantify the thermal environment of humans and the energy fluxes between body and environment. Compared to open spaces/landscapes the complex surface structure of urban areas creates an environment with special microclimatic characteristics, which have a dominant effect on the energy balance of the human body. In this study, outdoor thermal comfort conditions are examined through two field-surveys in Szeged, a South-Hungarian city (population 160,000). The intensity of radiation fluxes is dependent on several factors, such as surface structure and housing density. Since our sample area is located in a heavily built-up city centre, radiation fluxes are mainly influenced by narrow streets and several 20–30-year-old (20–30 m tall) trees. Special emphasis is given to the human-biometeorological assessment of the microclimate of complex urban environments through the application of the thermal index PET. The analysis is carried out by the utilization of the RayMan model. Firstly, bioclimatic conditions of sites located close to each other but shaded differently by buildings and plants are compared. The results show that differences in the PET index amongst these places can be as high as 15–20 ∘ C due to the different irradiation. Secondly, the investigation of different modelled environments by RayMan (only buildings, buildings + trees and only trees) shows significant alterations in the human comfort sensation between the situations.