IMPORTANCE: Young adults with a childhood history of parental incarceration (PI) or juvenile justice involvement (JJI) are more likely to have worse mental health outcomes than their peers. However, the association between mental health and exposure to both PI and JJI (PI plus JJI) is unclear. OBJECTIVE: To determine the association of PI plus JJI exposure with mental health outcomes in young adulthood. DESIGN, SETTING, AND PARTICIPANTS: A cross-sectional study of the US National Longitudinal Survey of Adolescent to Adult Health was conducted to examine the associations between PI, JJI, and PI plus JJI and mental health outcomes (ie, depression, anxiety, posttraumatic stress disorder, suicidal ideation, and mental health counseling). In-home interviews were conducted of 13 083 participants; 704 participants with PI after age 18 years were excluded, and 12 379 participants formed the analysis sample. Participants were in grades 7 to 12 in 1994 to 1995 and were ages 24 to 32 years at follow-up in 2008. Data analysis was completed in 2019. EXPOSURES: Parental incarceration, JJI, or PI plus JJI before age 18 years. MAIN OUTCOMES AND MEASURES: Mental health outcomes in early adulthood (ages 24-32 years). The analysis included multivariable logistic regression models; accounted for individual, family, and geographic-level factors; and generated adjusted odds ratios. RESULTS: Among 13 083 participants (6962 female; weighted proportion, 49.6%) with a mean age at wave 1 of 15.4 years (95% CI, 15.2-15.7 years), 10 499 (80.2%) did not have a history of PI or JJI, 1247 (9.1%) had childhood PI, 704 (5.2%) had PI after age 18 years, 492 (4.5%) had JJI only, and 141 (1.2%) had PI plus JJI. Sociodemographic characteristics varied by exposure. Exposure to both PI and JJI was associated with a greater risk of depression (adjusted odds ratio, 2.80; 95% CI, 1.60-4.90), anxiety (adjusted odds ratio, 1.89; 95% CI, 1.08-3.31), and posttraumatic stress disorder (adjusted odds ratio, 2.92; 95% CI, 1.09-7.82) compared with peers with neither exposure. Exposure to both PI and JJI did not have an additive association with mental health beyond PI or JJI alone. CONCLUSIONS AND RELEVANCE: This study suggests that exposure to the criminal justice system during childhood places individuals at risk for poor mental health outcomes in early adulthood. Clinical, advocacy, and policy efforts that prioritize reducing the impact of the US criminal justice system on children may yield substantive improvements in the mental well-being of those individuals as adults.