Resting blood pressures were recorded for children in the Dunedin Multidisciplinary Health and Development Study at two year intervals five times from age seven to fifteen. Correlations between pairs of readings were modest but significant, and higher for systolic (0.39 to 0.62) than for diastolic blood pressure. However, although children with normal blood pressure were likely to continue to have normal blood pressure, high blood pressures at age seven, nine, eleven and thirteen were not stable--only 28% of those whose systolic blood pressure at age seven was in the highest 5% had two subsequent readings in the highest 5%. On the other hand 56% of those in the highest 20% had two subsequent readings in the highest 20%, and 9% had all subsequent readings in the highest 20%. We do not believe that adult essential hypertensives can be recognised early by annual blood pressure measurement in childhood and the assignation of blood pressure rank according to a set of normal values.