Antenatal sonography consistently reveals three parallel echogenic lines on high-axial scans of the fetal head. Previous descriptions of fetal intracranial anatomy assumed that the inner line originates from the interhemispheric fissure and that the outer lines originate from the lateral walls of the lateral ventricles. By studying the three lines sonographically in 25 fetuses and by injecting contrast material into the deep venous system of autopsy specimens, we showed that the outer two lines do not represent the lateral walls of the lateral ventricles, but rather appear to arise from deep intracerebral veins. This finding challenges the validity of lateral ventricular hemispheric ratios in the diagnosis of early hydrocephalus, since such calculations assume that the outer lines originate from the ventricular walls rather than from veins. The results of this study reveal that the two outer lines most likely originate from deep cerebral veins, rather than from the lateral walls of the lateral ventricles.