In this article the incidence of consensual unions in Poland is analysed. Demographic features of cohabitants, such as the place of residence, age, marital and parental status, and one economic feature - the main source of income, are of main interest. According to the 2002 Population Census, which provides this analysis with statistical data, the scale of cohabitation is very marginal and inconsiderable in the Polish population. Even though the number of consensual unions has risen twice since 1978, cohabitations amount only to 2.2 percent of all unions. Approximately every third consensual union in Poland is constituted by the young - aged 20-34 - and the never married. In this age group cohabitations are in particular popular, but still, however, the institution of marriage is the predominant type of partnership. This conclusion is supported by results of several sociological surveys quoted in the article. According to opinions of various groups of respondents, consensual unions are accepted as long as they constitute a temporary and short-lasting stage followed by marriage. The civil law, or rather possible obstacles in obtaining a divorce, is not a cause for entering consensual union. Most cohabitants are free to get married, but they do not wish to. Divorcees constitute a very numerous group of Polish cohabitants. Persons, who have already terminated marriage, more often prefer living in consensual union to entering the remarriage. Cohabitants have on average fewer children than married persons. Almost 200 thousand children, which is as low as 1.6 percent of all persons aged 0-24 in Poland, live in families constituted by a cohabiting couple. Both statistical data and results of the quoted sociological researches reflect the fact that marriage is the only accepted institution for having and raising children. In comparison with the overall Polish population, cohabitants are more prone to being dependants of other households or to living on unemployment and welfare benefits. This may result in economic instability and in lower status of consensual unions. The main conclusion of the article is that marriage is still the prevalent type of union and the only widely-accepted family-building institution in Poland. Cohabitation may be widespread among certain social groups, but in the whole society it is still marginal. That marginality discourages social scientists from studying the incidence of consensual unions in details. According to the 2002 Population Census, the picture of that phenomenon is very ambiguous and differentiated and, thus, it is worth analysing.