Background. The corpus callosum comprises the largest tract of nerve fibres in the human brain. It is developed from th e telencephalon starting in the 11th week of foetal life. Partial or complete agenesis of the corpus callosum is a rare developmental anomaly of unknown cause. A case of corpus callosum agenesis is described. Case report. The patient was a small for gesta tional age (1950g) female infant delivered at 35 weeks. In view of multiple congenital abnormalities (bilateral choanal atresia, atrial septal defect, ventricular septal defect and facial dysmorphism), chromosome studies were done and showed partial monoso my of chromosome 13 (46,XX, del (13)(q22q33) ). Head ultrasound and cranial CT scan was performed which found appearances typical of agenesis of the corpus with ascension of the third ventricle and increased distance between lateral ventricles, cerebellar hemispheres and vermis atrophy, cisterna magna and fourth ventricle dilatation. After the surgical intervention for bilateral choanal atresia, a cranial ultrasound was performed and confirmed the atresia of the corpus callosum, but the path of anterior cer ebral artery showed on color Doppler suggests the existence of the rostrum. The patient was carefully monitored after the surgery. 24 days after the surgery the general status of the patient becomes altered, the patient presenting jet vomiting and nystagmu s. The transfontanellar ultrasound showed ventriculomegaly with intracranial pressure (IR: 0.79 -->0.95) and the lumbar puncture showed transparent, sterile cerebrospinal fluid for which she remains carefully monitored. Conclusions. Although rare, agenesis of the corpus callosum is easely recognisable on CT scan and neonatal ultrasound. Even it is itself asymptomatic, may be associated with other malformations, especially in genetic syndromes, playing an important role in the production of neurological sympt oms.