Most European countries have seen a retreat from marriage, which is increasingly preceded or replaced by cohabitation. A question that arises in light of this trend is how the diffusion of non-marital cohabitation may affect the quality of family relations. This article investigates how cohabitation among young people affects their level of satisfaction with their relationship with their parents. We analyse data from the recently released Generation and Gender Survey for Poland, a country with a limited degree of social acceptance of cohabitation, a high degree of attachment to the institution of marriage, and a familialistic culture. Since young adults who choose to cohabit are a rather specific group, we use statistical methods that allow us to control for both the observed and the unobserved characteristics of cohabiters. We find that young people who cohabited in their first union rated their level of satisfaction with their parental relationship lower than their peers who were married. Thus, at least in the context of a country where informal partnerships are not yet fully socially accepted or institutionally supported, the role of cohabitation in intergenerational relations may not be neutral.