Obesity and hypertension are two of the major risk factors for cardiovascular disease (CVD) and those with obesity have a greater risk of hypertension. In children and adolescents, high body mass index correlates with elevated blood pressure. Genetic factors make a significant contribution to the variation of obesity and hypertension. The investigators will address how genetic and environmental factors influence the co-occurrence of obesity and hypertension during development and aim to identify cardiovascular risk factors in adolescence that will predict CVD in adults. Genetically informative cardiovascular and anthropometric data from childhood to young adulthood will help answer these questions. The investigators have access to two major longitudinal population-based adolescent twin-family datasets, the Medical College of Virginia Twin Study [CVT] (Dr. R. Schieken) and the Leuven Longitudinal Twin Study [LLTS] (Prof. Dr. G. Beunen). The CVT is a longitudinal population-based study of Virginian 570 twin pairs (and parents) measured from age 11 to 17 on cardiovascular risk factors. The LLTS is a longitudinal population-based study of 105 Belgian twin pairs and parents with anthropometry, cardiovascular and fitness assessments between ages 10 and 18. Genetic epidemiologic methods provide information about the causes of the variation and covariation, and the direction of causation between variables. Availability of longitudinal twin-parent data further strengthens our design. The investigators will analyze anthropometric, cardiovascular, physiologic and physical fitness data to investigate a series of critical issues about the etiology, heterogeneity, comorbidity and developmental trajectories of CVD risk factors, including obesity, hypertension and cardiovascular health. With these two exceptional datasets, they will investigate the main questions of this application: How do genes and environment act and interact to create covariation between obesity and hypertension, and are the genetic and environmental factors the same at all ages (from childhood to late adolescence and adulthood) in both sexes? Areas of research will include the following: causes of individual differences in anthropometric and cardiovascular characteristics, their covariation and developmental change or continuity in adolescence, parent-offspring transmission, prediction of cardiovascular risk, and sex, race and population differences in genetic and environmental contributions on cardiovascular risk factors. The investigators point out that given that heart disease begins in childhood, a better understanding of the development of cardiovascular risk is vital for the treatment and prevention of CVD.