In Croatian legislation, the extramarital cohabitation is considered to be a life community of an unmarried man and unmarried woman, witch lasts for at least three years or less in the case that a common child is born or if such community continues by marriage. The extramarital cohabitation creates personal and property effects as a marriage. It applies to the provisions of the Family law on personal and property relations of married companions. The basic characteristic of the extramarital cohabitation and the fundamental difference in relation to the marriage is its informality. Nevertheless, in the Croatian legal order it enjoys great legal protection. Because of its informal way of establishing and terminating and due to the inequality of legal regulations, courts have been left to establish the existence of cohabitation II and the existance of preconditions for its legal protection. Extramarital companions often come into the situation that acording to the one regulation they fulfill preconditions necessary for the realization of rights and obligations, and according to the second regulation they do not. As a consequence of all that, there is appearance of legal uncertainty in proving the extramarital cohabitation.