As adolescents spend increasing amounts of time away from home, parental trust should become important. Little is known about how trust develops, however. We propose that parental trust is primarily based on knowledge. In this study, we pitted three types of knowledge of the child against each other in the prediction of parental trust: knowledge of feelings and concerns; of past delinquency; and of daily activities. Results showed that knowledge of daily activities was more important than knowledge of past delinquency. In further analyses, knowledge of daily activities that came from the child's spontaneous disclosure was most closely linked to parental trust. These findings add support to a recent re‐interpretation of parental “monitoring” as parental knowledge that mainly comes from spontaneous child disclosure. Additionally, the role of parental trust for dysfunctional family relations was examined and it was found that the relations between the child's delinquency and family dysfunction were mediated by parental trust. Finally, even though there was substantial agreement between parents and children about parental trust in the child, the individual's unique perspectives were important. Family dysfunction from the child's perspective was based on whether they believed that their parents trusted them, and parental perceptions of family dysfunction were based on their own trust in the child.