The Dutch legal system is primarily based on formal family and partner relationships. There is, due to a number of social trends, a growing divergence between family form and family function. In this article the laws on parentage will be analysed with respect to the relationship between fathers and children in informal relationships. This is of particular interest due to the increasing number of extramarital births, which presumably results in a growing number of biological and social fathers not having full parental legal status. Although the legal system is faced with urgent questions as a result of these social trends, the legislature has paid little attention to them. It will be questioned whether a change of the parentage law in informal family relationships could be helpful in dealing with the divergence between the status of formal and functional fathers in Dutch family law.