The sonographic findings in nine cases of agenesis of the corpus callosum examined before and after birth are reported. Agenesis of the corpus callosum was suspected in utero due to a typical configuration of the lateral ventricles, which included enlargement of the atria and occipital horns and marked separation of the bodies. In three cases pregnancy was terminated because of severe associated anomalies. In the remaining six cases postnatal ultrasound examination allowed a certain diagnosis by demonstrating the abnormal configuration of the lateral ventricles, varying degrees of enlargement, and upward displacement of the third ventricle and absence of the corpus callosum.