Seventy-three real time sonographic scans were performed through the anterior fontanelle of 67 infants between 28 and 48 weeks post-conception who had no evidence of intracranial disease. Several anatomical measurements were plotted against independent variables such as post-conception age, weight and head circumference at the time of the examination. All of the measurements increased as age, weight and head circumference increased. Ratios formed by dividing transventricular diameters by transcalvarial diameters at the two levels in the coronal plane and by dividing occipital mantle thickness by frontal mantle thickness in the parasagittal planes remained stable as all of the independent variables increased. In 88% of cases the occipital mantle could not be measured since the occipital horns of the lateral ventricles could not be identified. Since dilation of the ventricular system starts in the occipital horns of the lateral ventricles, non-visualization of this area is an important negative finding.