The blood pressure (BP) in children has been studied since the beginning of this century, and in the past decade the potential association between childhood BP levels and adult hypertension has gained increasing interest. From several longitudinal studies, many of them comprising large numbers of children and youngsters, it appears that the BP of children is significantly associated with BP on follow-up measurements and that childhood BP is related to adult levels. Whether the objective is to predict future BP, or the aim is to shed light on the early pathogenesis of primary hypertension, it is of major importance to find out why BP rises in some and stays the same in others. To achieve this, characteristics need to be detected that are related to changes in BP in the first decades of life. Although not many reports on these dynamic relations are presently available, age, height, body weight, initial BP level, and a family history of hypertension have been put forward as determinants of children's BP change over time. Moreover, there are data to support the effect of dietary factors, most notably certain electrolytes, on BP regulation early in life. Also, certain hemodynamic and neural characteristics, such as changes in cardiac output and left ventricular mass, renal blood flow, and sympathetic nervous system activity, may be related to a subsequent rise in BP and future hypertension. Findings from nonexperimental and experimental studies on determinants of BP in children and youngsters will be reviewed.