The author discusses the fifth phase of demographic transition and post-transitional periods in Poland and in some European countries. Basic demographic processes, especially fertility and mortality in Poland run a course similar to that in most developed countries. Since age-sex structure of Polish population is unregular the author presents basic properties of demographic structures and processes up to the year 2000. Discussion of the transformation of family size in Poland is presented on the basis of TFRs. At the beginning of the century the TFR was 6,2 children per woman of fertility age, in 1930-ties 3.5 and in 1980 only 2,3. Urban-rural differentiation presents that since middle of 1960-ties the expanded reproduction of population in Poland is due to women living in rural areas (Tabl. 2). Taking into consideration the analysis of demographic trends and expected socio-economic changes the author notes that despite a relatively high level of natural increase the existing level of fertility in Poland is approaching that assuring only a simple reproduction of generations, i.e. 215 children per 100 women aged 15-49. The author postulates that reproduction of generations should be counted among important strategic goals of the country's development. It would be advantageous to maintain the level of reproduction slightly above the level of a simple reproduction of generations. Finally, the author postulates that the socio-economic policy of the country should incorporate demographic strategic goals as goals of highest priority when new plans of socio-economic development are formulated. Digitalizacja i deponowanie archiwalnych zeszytów RPEiS sfinansowane przez MNiSW w ramach realizacji umowy nr 541/P-DUN/2016