This paper presents the divagations about conformity between „biological paternity” and „lawful paternity”. Among methods to determine paternity are mentioned: presuming that the mother’s husband is her child’s father, acknowledgment of a child and establishment of paternity in court. The 2004 amendment of Family and Guardianship Code lawfully vested a man claiming to be a biological father with the right to institute a paternity action. Unfortunately asserting rights at the court are impossible, when the paternity has been established in any other lawful ways. It inspire to considerations on rightness of such solutions and to introduce potential changes.