The lack of statistical sources available raises difficulties to estimate the net internal migration. Portugal is a country without a anual migration register, therefore, various approaches are taken to estimate the migration component. However, the results obtain ed by the proposed methodological frames were not satisfactory.
The present paper provides three methodological frames able to estimate the net internal migration component. The first considers constant, for ten years, the net internal migration obtained in the census moment. The second introduces a constant transition probability matrix that fits the migration flows to population. The third methodological frame lays in a stochastic transition probability matrix and is a model whit a total dinamic behaviour.
The constant matrix methodology seems to be the one that better solves the problem. Unfortunately, it´s not possible to prove that the methodological frame with a stochastic matrix produces better results.

keywords: net internal migration, transition probability matrix, stochastic process, Markov chain.