The true longitudinal correlations between parental monitoring and peer delinquency were often unclear since parental monitoring measurements evaluate parental knowledge rather than parental monitoring behaviors. The current sample included 1,095 male justice-involved teenagers (13–17 years old at baseline) from the United States who gave survey data every 6 months for 3 years. Random intercept cross-lagged panel models were used to evaluate between-individual and within-individual bidirectional impacts of parental monitoring variables (i.e., parental solicitation and monitoring regulations) and peer delinquency. Although there was a negative relationship between parental monitoring and peer delinquency on a between-individual level, there were minimal within-individual directional effects. Parental solicitation predicted increased peer delinquency, and peer misbehavior predicted fewer parental monitoring restrictions over time, according to the minimal within-individual effects found. While increased overall parental monitoring was linked to lower peer delinquency, there was limited evidence that improvements in parental monitoring lead to longer-term decreases in peer delinquency. The findings back up prior research, indicating that parental monitoring should not be the main intervention strategy for reducing peer delinquency.