The corpus callosum is the major interhemispheric commissure and its abnormalities include agenesis, partial agenesis, hypoplasia, hyperplasia and lipoma. Anomalies of the corpus callosum are commonly associated with other malformations, aneuploidies or genetic syndromes. Furthermore, even in isolated cases, the risk of abnormal neurodevelopment is high. Antenatal diagnosis of complete callosal agenesis is easy after midtrimester by ultrasound even in axial plane. More subtle findings (hypoplasia and partial agenesis) may also be recognized antenatally. In these situations sonographic diagnosis is very difficult because the axial view of the fetal head is often unremarkable and obtaining a true sagittal view usually needs more experience. Nomograms for fetal corpus callosal biometry have been published and are of critical importance for diagnosis of such subtle abnormal findings. When pathology of the corpus callosum is suspected fetal MRI is an important adjunct to sonography in evaluating its anatomy and associated anomalies. Many additional findings that are not visible by ultrasound such as abnormal sulcation and heterotopia can be identified by MRI.