This article used a sample of 2 adolescents per family to (a) examine the extent to which parental monitoring and adolescent information management are characteristics of families or of dyads and (b) replicate past research on parental monitoring and adolescent information management using models that distinguish differences between families from differences within them. Within- and between-family differences were examined as a function of parents (positive and negative parenting, immigration status), individual and peer-reported problem behavior, and adolescent characteristics (age, gender) in a sample of 300 Swedish families with 2 siblings each (aged 10 to 19). Parents' self-reports of their monitoring of siblings and of their adolescents' information management were consistently more similar than adolescents' self-reports or reports on parents. Siblings' reports of parental monitoring and self-reports of routine and personal information management were modestly related to one another. Reports of secrecy, however, were statistically independent. Results predicting between-sibling differences are consistent with those obtained from longitudinal studies of one sibling per family: adolescents who engage in problem behavior are more secretive and disclose less information to parents. Their parents report them to be more secretive. Siblings who engage in delinquency report lower parent solicitation and control. Siblings' reports of both positive and negative parenting were associated with within-family differences in parental monitoring and their own information management. The results reinforce previous findings on the important role adolescents play in their own socialization. Differences between adolescent and parent reports highlight important methodological biases that may obscure key processes in family communication.