Familial aggregation of blood pressure in childhood and the difference between males and females were studied in a random sample of a nursery and school-age population in Milan. Age, sex, height, weight, skinfold thicknesses and heart rate were obtained. Blood pressure was measured in accordance with the recommendations of the Task Force of Blood Pressure Control in Children. After adjusting for age, significant correlation coefficients were found between mother and son (r = 0.17 and r = 0.11), mother and daughter (r = 0.11 and r = 0.15), and father and son (r = 0.16 and r = 0.17) for systolic and diastolic pressure, respectively; the father-daughter correlations were not statistically different (r = 0.08 and r = 0.03). Multiple regression analysis underlined the difference between males and females; height was an important determinant in the males and body weight in the females. In conclusion, anthropometric measurements should be considered in evaluations of blood pressure status. Our results suggest important differences between males and females. The BP pattern of the parents also seems more important for sons, and there seems to be a lower correlation between fathers and daughters.