Studies have been undertaken to investigate the directions of growth expressed at the chin and the mid-face and their orthodontic significance. This paper reports one part of this investigation in which the prevalence of various direction of growth of the chin and the mid-face were studied in two random samples of children, one taken from the serial experimental sample of the Burlington Growth Center and the other consisting of corresponding longitudinal material from the Center for Human Growth at Ann Arbor. The growth direction of the sub-nasale and gnathion were measured on superimposed tracings of lateral cephalometric radiographs from the age of six years onwards from the Burlington sample, and databank digitized values for the Ann Arbor material. Account was taken of errors arising from orientation, tracings and superimposition. The results showed a sex difference for growth of the chin and mid-face with slightly more horizontal growth in boys. The correlation between the growth direction of the upper and lower jaws did not depend on the use of SN-line as a common base line. Only 25—40% of the variability was due to factors common to both jaws which determine whether the growth pattern of the face will be generally horizontal or vertical. The growth direction followed by each jaw is to a large extent determined by independent factors. Prediction of growth direction or illustration of growth direction during and after orthodontic treatment from superimposed serial tracings is hazardous because of the errors involved. The low incidence of backward growing mandibles in a large random sample of the population compared to the prevalence of these problems reported in orthodontic practice can be partly explained by inappropriate orthodontic treatment. The superimposed tracings of all the individuals used in the Burlington sample did not show that the last increments of mandibular growth are horizontal. Horizontal increments of mandibular growth are usually seen following orthodontic treatment and probably represent recovery from a downward and backward mandibular rotation created during the treatment.