We draw knowledge about the society from various sources. Primary data are the most important: their dependability is the condition of credibility of the future analyses and publications. Moreover, as in case of the Polish National Census, it becomes the basis for governmental and parliamentary economic and social programs. The text underlines the benefits of the last census, its credibility as well as merits of the information it provides. It proved particularly helpful in case of a dramatic correction of the existing data regarding the scope of unemployment in Poland. Among the census' shortcomings we can find: the lack of basic data concerning the class structure of the society, economic and social diversification, educational opportunities of the children of famers, workers and intelligentsia. These are the kind of information, which are also not found in the Central Statistical Office databank.