This paper presents a comparison of the characteristics of the electricity demand for London, UK and Athens, Greece and explores its relationship with both climate and non-climate related factors. Year-to-year trends for both cities are identified, associated mainly with economic, social and demographic factors. In addition, several other effects such as weekly and holiday effects, unrelated to weather conditions are detected and are examined in comparison for the two cities. Gross National Product (GNP) per capita has been employed to aid de-trend the data in order to isolate the weather/climate influence on electricity demand. Temperature has been found to play the most important role in controlling the electricity load demand, especially for Athens. For both cities electricity demand peaks in winter but for Athens a second significant peak is apparent in the summer, not present in London. Thermal comfort levels for both cities have also been identified and compared. The optimum ambient temperature for low levels of electricity demand is found to be 20 degrees C for Athens and 16 degrees C for London. Using the approach of cooling and heating degree-days, it was identified that the sensitivity of the system electricity-demand/air-temperature is greater during the cold period of the year for both cities. (C) 2009 Elsevier Ltd. All rights reserved.