The population in the European Union has remained stagnant for many years. The continued decline in birth rate and increasing life expectancy are leading to an aging population. In Spain, this aging process has been accelerated. The Spanish case requires a complex multidisciplinary analysis to achieve a proper understanding of this population phenomenon that has serious consequences for Spain. This paper analyzes the causes of the aging population and its future consequences. Multiple data sources, mostly from the National Institute of Statistics and Ministry of Labour and Social Security, are used to support the analyses. For several years, many immigrants have arrived in Spain, resulting in a significant increase in population and a decrease in the rates of aging. A positive and intense migratory balance has stopped, and shows signs of change. Numerous elements indicate that the Spanish economy does not suffer a transient crisis situation; there is a depletion of the production model, hindering a quick exit from the situation of economic and financial crisis. In this context, it is not easy to get a new and favorable migratory balance. A significant Spanish demographic weakness is confirmed; the population structure has not changed despite the recent intense immigration process. The threat of the demographic regression is announced in a near temporal horizon.