Blood pressure in young adults predicts blood pressure in later life. We aimed to identify metabolic, haemodynamic and autonomic characteristics associated with raised blood pressure in young adults and whether these differ between males and females. 3145 healthy subjects, aged 18-40 years, were grouped according to sex and blood pressure category following the recent reclassification of blood pressure as part of American Heart Association/American College of Cardiology 2017 guidelines. All individuals undertook a lifestyle and medical history questionnaire, and detailed metabolic, haemodynamic and autonomic assessments. Stage 1 hypertension and normal blood pressure were the most common blood pressure phenotypes in males (29%) and females (68%), respectively. In both sexes, cardiac output was positively associated with increasing blood pressure category (P<0.001 for both). Similar positive trends were observed for heart rate and stroke volume in males (P<0.001 for both) and heart rate in females (P<0.001). Unlike in males, peripheral vascular resistance, aortic pulse wave velocity and augmentation index were significantly increased in hypertensive females (P<0.001 for all) compared with the other blood pressure categories. Most heart rate variability indices decreased across the blood pressure categories, particularly in males. In young adults, metabolic and haemodynamic abnormalities associated with hypertension are already present at the elevated blood pressure stage and the overall phenotype differed markedly between sexes. While a “cardiac” phenotype was associated with elevated blood pressure and hypertension in males, a “vascular” phenotype, characterized by elevated peripheral vascular resistance, aortic pulse wave velocity and augmentation index, was dominant in females.