Identifying individuals at a young age who are at risk for future development of hypertension in adult life is a public health issue of great importance. The imperfect nature of blood pressure tracking throughout childhood and adolescence, and the fact that the genes which determine blood pressure in childhood may not be the same ones which operate in adulthood make it clear that improved predicting models are needed. The twin-parent study design allowed testing more subtle genetic and environmental hypotheses than was possible with nuclear families or twins alone. The longitudinal component permitted an analysis of developmental changes in the genetic expression of the hemodynamic determinants of blood pressure. The inclusion of unlike sex twins permitted an analysis of the consistency of genetic and environmental effects across the sexes.