This multi‐informant longitudinal study aimed to understand whether the family dynamics that underlie adolescent voluntary disclosure regarding their leisure time behavior differs when adolescents strongly or weakly endorse the legitimacy of parental authority. Longitudinal linkages between parental monitoring behaviors and adolescents' secrecy and disclosure were tested among youths with strong and weak legitimacy beliefs. The sample included 197 adolescents (51% female, M age 12 years) and their mothers. Mothers reported on several of their own monitoring efforts (i.e., solicitation, active involvement, observing and listening, and obtaining information from spouses, siblings, and others). Adolescents reported their disclosure, secrecy, and legitimacy beliefs. Only among youths reporting strong legitimacy beliefs, more mother engagement and supervision (indexed by mother‐reported active involvement and observing and listening) predicted more adolescent disclosure and less secrecy over time, and more mother solicitation predicted less secrecy.