As part of an epidemiological study on cardiovascular risk factors among children and adolescents in Navarra, arterial blood pressure (BP) readings were taken in 5,829 children, including both sexes and aged between 4 and 17 years. The subjects were randomly selected from the public and private school population in our community. BP-age and BP-height percentiles were obtained for each sex and the physiological variations in BP according to these parameters was also analyzed. Systolic BP increased with age in both sexes throughout childhood. During adolescence, there is almost no variation in BP among girls, but in boys older than 13 years, there is a sudden increase. For this reason, boys have higher values than girls. Diastolic BP shows a linear increase in both sexes. BP increases with height in both sexes. In spite of the sudden rise in systolic BP among the boys taller than 145 cm, the increase in systolic BP in relationship to height is smaller and more homogeneous than the increase seen with age. As the BP variations with height are smaller and more homogeneous than those related to age, it is preferable to evaluate this parameter by BP-height rather than by BP-age.