Familial aggregation of blood pressure (BP) was studied in 545 families, of which 370 included natural children only, 24 adopted children only and 175 both natural and adopted children. Mean values of four Automatic BP measurements (Dinamap 845) were converted into age (adult) or height (children) and sex adjusted scores. One comparison per family between parents and randomly chosen index children were made. A significant resemblance of blood pressure is observed between natural children and their parents: Systolic BP r = 0.24. Diastolic BP r = 0.29. N = 272 p less than 0.05. Adopted children did not have BP resemblances to the mean BP values of their parents but a significant resemblance was found between children and their mothers for a small sample (N = 46). Weight, heart rate, age and duration of cohabitation do not influence the results. A familial influence on BP can be detected in children. However, estimating the relative contribution of genetic and common environmental factors to BP correlations between family members is difficult. Nevertheless, the BP of children whose parents have high BP should be monitored.