The publication is composed of three chapters structured as follows: the first chapter contains the methodological aspects inherent in the calculation of post-census estimates; the second chapter analyses the main results and identifies some of the possible causes of the observed population dynamics; the third chapter presents estimates by gender and large age groups and the major indicators, referring to Portugal, NUTS 1, NUTS 2, NUTS 3, municipalities and districts for 1991-2000, as well as the population by age, year on year, for Portugal and NUTS 2.