BackgroundPrevious studies have analyzed the relationship between screen time and cardiometabolic disease risk factors among adolescents, but few have examined the longitudinal effects of screen time on cardiometabolic health into adulthood using nationally representative data.ObjectiveTo determine prospective associations between screen time and later cardiometabolic disease over a 24-year period using a nationally representative adolescent cohort.DesignLongitudinal prospective cohort data from the National Longitudinal Study of Adolescent to Adult Health (Add Health) collected from 1994 to 2018.ParticipantsAdolescents aged 11–18 years old at baseline (1994–1995) followed for 24 years.Main MeasuresPredictors: screen time (five repeated measures of self-reported television and video watching from adolescence to adulthood). Outcomes: Five repeated measures of body mass index (BMI); two repeated measures of waist circumference, hypertension, hyperlipidemia, and diabetes collected at 15- and 24-year follow-up exams.Key ResultsFor the 7105 adolescents in the sample (49.7% female, 35.0% non-white), the baseline adolescent average screen time per day was 2.86 ± 0.08 hours per day, which generally declined through 24-year follow-up. Average BMI at baseline was 22.57 ± 0.13 kg/m2, which increased to 30.27 ± 0.18 kg/m2through follow-up. By 24-year follow-up, 43.4% of participants had obesity, 8.4% had diabetes, 31.8% had hypertension, and 14.9% had hyperlipidemia. In mixed-effects generalized linear models, each additional hour of screen time per day was associated with 0.06 (95% CI 0.04–0.09) within-person increase in BMI. Each additional hour of screen time per day was associated with higher within-person odds of high waist circumference (AOR 1.17, 95% CI 1.09–1.26), obesity (AOR 1.09, 95% CI 1.03–1.15), and diabetes (AOR 1.17, 95% CI 1.07–1.28). Screen time was not significantly associated with hypertension or hyperlipidemia.ConclusionsIn this prospective cohort study, higher screen time in adolescence was associated with higher odds of select indicators of cardiometabolic disease in adulthood.Supplementary InformationThe online version contains supplementary material available at 10.1007/s11606-022-07984-6.