Relationships between the health insurance status and healthcare use among justice-involved youths transitioning into adulthood is an underexplored topic, even if transition to adulthood is a crucial time period for healthcare outcomes. To fill in these knowledge gaps, this study had two aims: (1) to examine trajectories of health insurance coverage and healthcare use among serious juvenile offenders transitioning into adulthood; and (2) to explore associations between the lack of health insurance, healthcare use and reincarceration.