In 236 schoolchildren aged 7-15 years arm blood pressure was measured using a semiautomatic technique. Three different cuffs were chosen among four cuffs with bladder sizes of either 6 x 20 cm, 9 x 27 cm, 12 x 35 cm or 15 x 43 cm. Ideal cuff size in each pupil was defined as the one in which the width of the bladder was closest to 40% of arm circumference. In all subjects ideal cuffs were tested along with two cuffs bigger or smaller than the ideal one. The study showed that "normal blood pressure" in relation to age depended on the cuff used. Using the ideal one, systolic blood pressure increased from 105 mmHg at 7 years of age to 117-119 mmHg at age 11, with no further increase at higher ages, while diastolic blood pressure was almost unchanged in the different age groups. Normal blood pressure curves constructed using the same cuff in all children showed a steeper increase in both systolic and diastolic blood pressure in relation to age compared to the curve based on the ideal cuff in all children. It is strongly recommended that future studies should take the best-suited cuff problem into consideration when planning studies among children. Some of the differences between previous published studies may be explained by the differences introduced by different cuff sizes.