Key PointsQuestionIs incarceration of youths in adult correctional facilities associated with an increased risk of mortality through 39 years of age?FindingsIn this cohort study of 8951 youths, incarceration in an adult correctional facility before the age of 18 years was associated with a 33% increase in the risk of mortality between 18 and 39 years of age.MeaningThis study suggests that incarceration in an adult correctional facility as a youth was associated with early mortality, potentially through diminished psychological and physical health.