Diastematomyelia is a rare spinal malformation characterized by a division of the spinal cord. More often, the two hemicords are separated by a midline and sagittal osseous or fibrocartilaginous spur. In this report we describe two cases of diastematomyelia detected at routine second trimester detailed sonography and further assessed by MRI and spiral CT with surface shaded 3D-reconstructions. In addition to providing diagnosis, prenatal evaluation helps differentiate between diastematomyelia with good or bad prognosis.