This paper looks at the energy efficiency of the Cité Frugès in Pessac, designed in 1924 by Le Corbusier. Many of the innovations introduced by the Modern movement, such as flat roofs, large windows and solar protection elements, are still evident in the way architecture is carried out today. Most of these contributions were implemented in the Cité Frugès. The aim is to evaluate the architectural design criteria that most influenced the energy performance of Le Corbusier’s works, and to analyse the improvement that could be achieved by energy rehabilitation. The methodology used consisted of a systematised study of the five dwellings designed by Le Corbusier. For the modelling and calculation of their energy performance the “Líder–Calener unified tool” was used for evaluation, under the standards of compliance with European regulations for nearly zero energy consumption buildings. Energy parameters, such as thermal transmittance, solar gains and overall annual energy demand, were tested. The results obtained provide information on energy performance and allow for the analysis of possible energy refurbishment alternatives. The analysis of the results makes it possible to identify and qualitatively and quantitatively assess the limitations of the most relevant architectural and construction aspects in relation to energy efficiency and to draw up an energy map of the Cité Frugès in Pessac.