Data on the growth of 1063 children and their parents were analysed. Of the variation in height at prepuberty about 20%, and of the final height 30-46%, were explained by the variation in parental heights; the children's own height at the age of 1.0 year increased the proportion explained to half. Two equations were developed for increasing the accuracy of the evaluation of growth. One defines parent specific mean height standard deviation score, and the other includes the parents' heights and the child's height at the age of 1.0 year and defines expected standard deviation score for height. These equations are easy to use if they are converted to nomograms.