A wide variety of weather-data are readily available for simulating buildings energy performance by using dynamic software. However, climate change and its effects on buildings energy performance represent a critical issue, also considering the implications of climate change on human comfort. Starting from this, the present study aims at analyzing the climatic conditions in Rome and its surroundings, evaluating the occurrence of the Urban Heat Island (UHI) phenomenon. Therefore, meteorological data derived from two airports near the city and climatic data registered for two years in a central, densely-built zone of Rome were analyzed and compared. Furthermore, the differences among weather data were tested by means of a commonly used dynamic software in order to evaluate the effects of different climatic boundary conditions on building energy performance, in terms of heating and cooling energy demands. The results highlight significant differences with regard to temperature, wind velocity and relative humidity, as a result of a prevailing UHI phenomenon in central Rome throughout the year. The simulations show an average increase of cooling energy demand of about 30% and an average reduction of heating energy demand of about 11%. Such differences give the rise for the investigation of the reliability of weather data files commonly used in building simulations, in order to properly estimate the buildings energy demand under a sustainable city perspective. (C) 2017 Elsevier B.V. All rights reserved.