As soon as blood pressure (BP) values are available for a child or teenager, a multitude of questions arise. The values obtained need to be interpreted, validated, and made use of. Values measured in an individual can be interpreted only by comparison with the results of measurements performed using the same protocol in an adequate sample of subjects with similar life styles. The value of reference to stature rather than age has been well established. Studies of BP measured at rest are the most widely used. The validity of blood pressure values is dependent on measurement technique but is also related to the problem of intraindividual variability. To address this problem, blood pressure values have been measured not only at rest but also during standardized stimulation tests and throughout the 24-hour period (ambulatory BP measurements). Studies using these techniques in children and adolescents are still scant. Longitudinal studies of the mean-term and long-term reproducibility of these measurements are needed. Until results of such studies are available, blood pressure measurements in non-resting subjects will be mainly useful for evaluating patients with borderline BP values at rest and for monitoring the effect of therapy. The response to blood pressure values believed to be borderline should include evaluation of factors which influence BP values as well as of the other risk factors for cardiovascular disease. The predictive value of blood pressure levels is fairly poor in childhood. Correlation coefficients between values obtained five years apart approximate 0.25. These coefficients increase with age and finally level off at 0.4-0.5.(ABSTRACT TRUNCATED AT 250 WORDS)