Indirect blood pressure (BP) was measured by mercury sphygmomanometer on 3524 children, ages 5-14 years, representative of a defined geographic population. Year 1 to Year 4 correlations ranged from 0.52 to 0.63 systolic blood pressure (SBP) and from 0.23 to 0.45 diastolic 4th phase blood pressure (DBP4). Some 55% of those originally in the upper decile remained in the uppermost two deciles 3 years later. All children ages 5, 8, 11, and 14 years were reexamined annually, and the mean year-to-year standard deviation (SD) within the child was computed to be 5.5 mm Hg SBP and 5.9 mm Hg DBP. After 3 years, for all available children (n = 2601) the age-specific cross-sectional SD was found to be 8.7-9.7 mm Hg SBP and 7.6-8.0 mm Hg DBP. These data enabled us to quantify the regression to the mean due to within-child variation for the uppermost and the lowest decile BP, using the Gardner-Heady model. These children had an average BP at examination that differed from the expected level (adjusting for regression to the mean due to within-child variation) by 1 mm Hg SBP and DBP. Quantification of the degree to which children's BP "tracks" is important for early diagnosis and intervention in high BP.