The Windsor Tower in Madrid was involved in a major fire, on 12-13 February 2005, which caused extensive structural damage to the upper floors of the building. This fire has provoked intense interest amongst researchers hoping to better understand the performance of conciete structures in fire. A research team integrated for Group GIDAI (University of Cantabria - Spain) and BRE Centre for Fire Safety Engineering (The Edinburgh University) has begun a study with the purpose of properly characterising the fire and the performance of the structure. The objectives of the study are (1) to analyze the fire growth conditions in order to understand the fire propagation mechanisms between floors of the building, using computational fire modelling, and (2) to evaluate the response of the structure to the fire. The research undertaken on the fire propagation on the 21 st floor, the origin of the fire, has allowed assessment of the severity conditions reached as consequence of the fully-developed fire, due the combustion of the present flammable materials. Starting from these results, characteristic curves of heat release rate representative of the real fire have been determined, to facilitate study of the thermal attack (temperatures, heat flux, etc.) on the structural elements. The tools used for this purpose were the Fire Dynamics Simulator (FDS) LES code, developed at the National Institute of Standards and Technology (NIST), and the SOFIE RANS code. These results will allow, in the next stages, to make use of finite element methods to obtain the corresponding thermal and mechanical state (stress and strain) of each element due to these conditions.