The purpose of this article is to present a basic data about aging of Polish society on the background of aging of European Union population. The article presents contemporary state and projections concerning process of aging, as well as its causes and the most important results. The basic impact on ageing is rendered by decrease of number of birth which results in changes proportion of youngest and oldest groups in the society. In the same direction affects the growth of life expectancy, entailing by reducing of mortality, particularly in the oldest demographic groups. In the case of Poland and majority of „new” EU’s members, aging population as the result of downfall of fertility rate and reproduction of population rate, is speeded up and deepened by minus net migration. Aging of the population is presently more advanced in former U–15, however, the pace of this process in last two decades is faster in “new” member states. Poland belongs to these EU states, which are threatened by demographic senility and depopulation the most and at the same time its demographic transformation is performing particularly dynamic. It causes that a passage between relatively advantageous demographic situation, that characterized Poland even in the eighties of 20–th century, and projected after 2020 dynamic population decrease, is being performed in relatively short time. Therefore, aging of population should be regarded as one of the most important and hard to be decided socioeconomic problems of contemporary Poland.