Objective: To examine criminal justice system (CJS) interactions and pathways through the justice system for young adults with ADHD compared to young adults without ADHD. Method: Nationwide 3-year birth cohort study using linked health and CJS data. Cox proportional hazards models were employed to examine associations between ADHD and police proceedings, court charges, court convictions, and incarcerations. Results: Young adults with ADHD were significantly more likely to interact with the CJS including police proceedings (hazard ratio [HR], 2.1 95% CI [2.0, 2.2]) court charges (HR, 2.2 95% CI [2.1, 2.3]), court convictions (HR, 2.3 95% CI [2.2, 2.4]), and incarceration (HR, 4.8 95% CI [4.3, 5.4]). Conclusions: Young adults with ADHD are overrepresented at all stages of the CJS. Results highlight the importance of early identification and responsivity to ADHD within the CJS and suggest that the NZ justice system may require changes to both areas to ensure that young individuals with ADHD receive equitable access to, and treatment within, the CJS.