Sonographic features are described in 6 infants in whom total or partial agenesis of the corpus callosum was confirmed by either computed tomographic or pathologic examination. The 6 patients demonstrated a range of abnormalities involving the neuraxis as well as other systems, notably cardiovascular, gastrointestinal and genitourinary. Chromosomal abnormalities were present in 2 patients. The sonographic features of callosal agenesis seen in these patients included: lack of characteristic acoustic interfaces to define the corpus callosum on both coronal and sagittal sonograms; increased separation and parallelism of the bodies of the lateral ventricles; loss of the characteristic convexity of the medial border of the anterior horns of the lateral ventricles; variable prominence of the occipital horns of the lateral ventricles; variable degree of superior extension of the 3rd ventricle; alteration or absence of the cavum septi pellucidi; and radial arrangement of cerebral sulci about the prominent 3rd ventricle. Cases of partial agenesis may show the dysplasia features found in complete agenesis. Only some of the callosal echoes are present. The sonographic features of partial agenesis in 1 infant were not described before.