The energy performance of buildings are strongly dependent on climatic conditions. Climatic data are acquired by measuring stations, generally located outside of the city, hence their reliability in reproducing the thermal conditions inside the urban environment should be carefully addressed. This paper deals with the analysis of the urban climate in Rome, city characterized by a composite urban texture and a high variability of the residential building stock. Air temperature and relative humidity were monitored in different neighborhoods of the city and in a microclimatic station placed in a countryside area for one year in 2015. The monitoring allowed to quantify relevant microclimatic indicators and to use the data as input to predict the impact on the energy performance of a reference building. It was found that UHI is uniform in winter, while it is zone dependent in summer. UHI hourly intensities reached 10.5 and 7.8°C in winter and summer, seasonal UHI reched 1.5°C in city centre. Urban cooling and heating degree days showed relevant variations up to 26% respect to the countryside area. In terms of predicted energy performance, UHI causes a winter reduction up to 36% and a summer increase up to 42%. © 2017 The Authors. Published by Elsevier Ltd.