Importance: Studies linking the quality of parent-adolescent relationships with young adult health outcomes could inform investments to support these complex relationships., Objective: To evaluate whether consistently measured, modifiable characteristics of parent-adolescent relationships are associated with young adult health across multiple domains., Design, Setting, and Participants: This cohort study used data from waves I (1994-1995; ages 12-17 years) and IV (2008-2009; ages 24-32 years) of the US National Longitudinal Study of Adolescent to Adult Health. Of 20 745 adolescents enrolled in wave I, 15 701 of 19 560 who were eligible completed wave IV (response rate, 80.3%). Data analyses were conducted from February 2019 to November 2020., Exposures: Parental warmth, parent-adolescent communication, time together, relationship and communication satisfaction, academic expectations, and maternal inductive discipline as reported at wave I by adolescent participants., Main Outcomes and Measures: Wave IV participant-reported self-rated health, depression, stress, optimism, nicotine dependence, substance abuse symptoms (alcohol, cannabis, or other drugs), unintended pregnancy, romantic relationship quality, physical violence, and alcohol-related injury. Separate regression models were run for mother-adolescent and father-adolescent relationships while controlling for age, biological sex, race and ethnicity, parental educational level, family structure, and child maltreatment experiences., Results: A total of 10 744 participants (mean [SD] age at wave IV, 28.2 [1.8] years; 52.0% female; 67.3% non-Hispanic White) and 8214 participants (mean [SD] age at wave IV, 28.2 [1.8] years; 50.8% female; 71.9% non-Hispanic White) had valid sampling weights and complete data for mother-adolescent and father-adolescent relationship characteristics, respectively. Adolescents who reported higher levels of mother-adolescent warmth (β = 0.11 [95% CI, 0.06-0.15]), communication (β = 0.02 [95% CI, 0.00-0.04]), time together (β = 0.07 [95% CI, 0.05-0.09]), academic expectations (β = 0.05 [95% CI, 0.02-0.08]), relationship or communication satisfaction (β = 0.07 [95% CI, 0.04-0.10]), and inductive discipline (β = 0.03 [95% CI, 0.01-0.05]) reported significantly higher levels of self-rated general health in young adulthood. Adolescents who reported higher levels of father-adolescent warmth (β = 0.07 [95% CI, 0.03-0.11]), communication (β = 0.03 [95% CI, 0.01-0.05]), time together (β = 0.06 [95% CI, 0.03-0.08]), academic expectations (β = 0.04 [95% CI, 0.01-0.06]), and relationship satisfaction (β = 0.07 [95% CI, 0.04-0.10]) also reported significantly higher levels of self-rated general health in young adulthood. Adolescents reporting higher levels of all exposures also reported significantly higher levels of optimism and romantic relationship quality in young adulthood (β coefficient range, 0.02 [95% CI, 0.00-0.04] to 0.24 [95% CI, 0.15-0.34]) and lower levels of stress and depressive symptoms (β coefficient range, -0.07 [95% CI, -0.12 to -0.02] to -0.48 [95% CI, -0.61 to -0.35]). Higher levels of parental warmth, time together, and relationship or communication satisfaction were significantly associated with lower levels of nicotine dependence (odds ratio range, 0.78 [95% CI, 0.72-0.85] to 0.89 [95% CI, 0.81-0.98]) and substance abuse symptoms (incidence rate ratio range, 0.60 [95% CI, 0.50-0.73] to 0.94 [95% CI, 0.89-0.99]), as well as lower odds of unintended pregnancy (odds ratio range, 0.81 [95% CI, 0.74-0.88] to 0.93 [95% CI, 0.86-0.99]). Patterns were less consistent for physical violence and alcohol-related injury. Characteristics of mother-adolescent and father-adolescent relationships were similarly associated with young adult outcomes., Conclusions and Relevance: The findings of this cohort study suggest that adolescents' positive perceptions of their relationships with their mothers and fathers are associated with a wide range of favorable outcomes in young adulthood. Investments in improving parent-adolescent relationships may have substantial benefits for young adult population health.