Blood pressure was continuously monitored over 24 h in 33 healthy children and adolescents (18 girls, 15 boys, age 6-17 years) using a portable monitor. The results were compared with European blood pressure centiles for normal children and adolescents. On average, 67% (57-88%, median and quartiles) of the measurements were completed. The day's mean for systolic blood pressure for girls was 0.04 (-0.67-1.00) standard deviations above the mean of the reference group with corresponding body-height, and for diastolic blood pressure, 1.08 (0.50-1.63) standard deviations. The corresponding values for boys were 0.42 (0.09-0.45) for systolic and 1.11 (1.00-1.39) for diastolic blood pressure. Mean systolic blood pressure for girls decreased during the night by 10% (5-13%) compared to the day time measurements, and the diastolic blood pressure decreased overnight by 23% (12-28%). Systolic blood pressure for boys decreased overnight by 8% (6-11.5%), and diastolic blood pressure decreased by 15% (12-19%).