The essays analyse the issue of paternity suits in the long run. For centuries, paternity could only be supposed and regulated by the law. Since the middle of the 20th century, the rule of law has been challenged by the scientific progress of biology and Dna tests, which prove paternity for sure. The issue has been related to fathers’ and mothers’ responsibilities for the livelihood of their illegitimate children. The prohibition of paternity suits was introduced by the French Revolution and confirmed in the civil codes of the XIX century, which have entrusted to mothers full responsibility for the care of children born outside marriage. Over the years, the feminist movement fought against this legislation, but only the reforms of family legislation (in Italy in 1975) attributed equal responsibilities to both parents and eliminated legal distinctions between legitimate and illegitimate children. Today Dna tests as proof of paternity open new conflicts between two established rights: the one of the children to take cognisance of their origin and the right of privacy of the parents.