For 284 students aged 8 to 15 years, systolic and diastolic (K4 and K5) blood pressures (BPs) were measured 3 times using a random-zero sphygmomanometer at each of 4 consecutive weekly visits. For systolic, K4 and K5 measurements, between-visit variability was greater than within-visit variability. Both between- and within-visit variability were least for systolic BP, and greatest for the K5 determination of diastolic BP. BP variability showed no significant relationship to age or sex. There was an inverse relation of both between- and within-visit variability to the level of diastolic BP for both K4 and K5 values, but variability was not related to the level of systolic BP. These data suggest that greater accuracy in the measurement of childhood BP can be achieved by taking multiple measurements at several consecutive visits. Consideration of BP variability is necessary to interpret epidemiologic data and to make clinical decisions about the diagnosis and management of children with hypertension.