This 3-year, multi-informant study examined whether youths' perceptions of parental privacy invasion predicted lower parental knowledge over time, as a function of increased adolescent secrecy. Participants were 497 Dutch adolescents (Time 1 M = 13 years, SD = 0.5; 57% boys) and both parents. Higher youth-reported invasion predicted lower father- and mother-reported knowledge 1 year later. A link between privacy invasion and youths' increased secrecy mediated the association between privacy invasion and mothers' lower knowledge. Further, mothers' perceptions of adolescent secrecy mediated the association between adolescent-reported secrecy and mothers' knowledge. No mediation existed for father-report models. The results suggest that privacy invasion is counterproductive to parents' efforts to remain knowledgeable about youths, due to increased adolescent secrecy. We discuss the implications for family communication processes and successful privacy negotiations during adolescence.