Unlike in older people, it has been suggested that elevated blood pressure (BP) in young people is because of high cardiac output accompanied by normal total peripheral resistance (TPR)—a hyperkinetic/hyperdynamic circulation. We investigated this in a large, United Kingdom-based birth cohort of adolescents. The study was conducted on 2091 17-year-old participants in the ALSPAC (Avon Longitudinal Study of Parents and Children)—a prospective population-based birth cohort study. BP measurement and echocardiography were performed, and heart rate (HR), stroke volume (SV), and TPR were calculated. Data are means (SD). Higher quintiles of systolic BP were associated with higher SV, higher HR, and higher TPR. The proportional contribution made by SV, HR, and TPR to mean arterial pressure differed little by systolic BP quintile (SV [32%–34%], HR [25%–29%], and TPR [39%–41%]). Higher BP is attributable to a combination of higher cardiac output (ie, SV×HR) and higher TPR in a population-based sample of adolescents. There is no evidence of a disproportionate contribution from elevated cardiac output at higher BP levels.