This paper addresses urban heat vulnerability in Mediterranean cities, by proposing and testing an approach that integrates the spatial distribution of mean radiant temperature (MRT) into the heat vulnerability index (HVI). Six typical neighbourhoods of the city of Rome are taken as a model of compact urban fabric. Socio-economic and environmental data were collected at the census-tract level, and MRT spatial analyses were conducted. The data were then aggregated to develop the three main components of the HVI: the Exposure map, the sensitivity map, and the adaptive capacity map. To assess the impact of MRT on the HVI, one scenario including and another one not including MRT were compared. The results highlight the importance of incorporating MRT in evaluating heat vulnerability, as this factor considers people’s perception of thermal comfort. It is evident that in dense urban forms, the integration of MRT in the HVI assessment leads to a reduced value of vulnerability, since shadows from the building help increasing outdoor thermal comfort. Conversely, in districts with large open areas, vulnerability values increase due to direct solar radiation and decreased thermal comfort. Additionally, the study demonstrates how the HVI can serve as a valuable tool for defining neighbourhood-oriented urban microclimate adaptation strategies.