Over the period 2001-2009, Portugal experienced a population growth at a weak and decreasing rate. This growth results almost exclusively of the net migration, since the natural change is very low, becoming, in average, negative in last three years. Fertility remains at levels far below those needed to renew the generations, longevity increases, and both these factors strengthen the process of demographic ageing.
The new family models in Portugal are the result of the significant fall in the number of marriages and the strong rise of the number of wedlock births, the number of divorces and the average age at marriage.
This paper intends to study the patterns of demographic variables responsible for the major changes in both population size and age structure of the population and culminating in its significant ageing.

keywords: population, fertility, mortality, life expectancy, migrations, ageing.