Building on previous research, this article investigates whether discrepancies between official and self-reported measures of arrests as an adult can be predicted from such discrepancies as an adolescent. We use longitudinal data from the Rochester Youth Development Study to assess whether a pattern exists in adolescent and adult under- and over-reporting of arrests. We find consistency in under- and over-reporting throughout the adolescent–young adult life course. In other words, when respondents misreport the number of arrests they have experienced, they do so consistently regardless of age. This is reassuring for scholars using self-report data, as under- and over-reporting behaviors remain stable over this span of the life course. Finally, our models predicting discrepancies in official and self-reported arrests during the combined period of adolescence and young adulthood are both extremely strong. Our findings support the continued use of self-report measures as a valid indicator of delinquency.