The extremely high temperatures recorded in Central Europe and in the northern and eastern of Spain during the summer of 2003 revealed the major impact that high temperatures have on public health. The excessively high death rates and hospital admissions related to these extreme temperatures have led to alert and prevention plans having been set out in our country in 2004 for the purpose of minimizing these effects. Fortunately, the temperatures recorded in 2004, which were much lower than in 2003, have not served to evaluate these plans in their full scope but have indeed served to detect some lacks which will progressively be corrected in the future. This article analyzes the mainly major impacts mainly of heat waves and also of cold waves. The socioeconomic factors having a bearing on these excessively high death rates and the measures set out which must be taken into account in the prevention plans. Particular stress is placed on the need of expediting the recording of disease and death rates in Spain and in the policies necessary for minimizing the impact on health of the extreme temperature events.