Knowledge of cooling degree-days is necessary in order to estimate the cooling requirements of buildings in a place, which characterize the overall temperature conditions during the summer period. Exact calculation of the cooling degree-days requires a long time series of hourly temperature. data from representative meteorological stations. In order to study the variability of the ambient temperature distribution in an urban environment, and the representativeness of a given station, cooling degree-days for three different meteorological stations located in the major Athens area have been calculated. An important spatial and temporal variability has been found. Problems related to the increase of the ambient temperature during the last 30 years are also studied. Finally, the accuracy of simplified methods to calculate the cooling degree-hours in a place is examined.