The antenatal diagnosis of isolated abnormalities of the posterior fossa is possible thanks to ultrasound screening and antenatal MRI, which are currently of excellent quality. The Arnold Chiari type 2 malformation is a rare congenital malformation of the cerebellum, it results from the normal growth of nerve elements in a posterior fossa too small. It is always associated with myelomeningocele. We report the case of an antenatal discovery, at 36 weeks of amenorrhea, of a Chiari type II malformation associated with a myelomeningocele. Through this case and a review of literature we will highlight the contribution of different methods of antenatal imaging in the diagnosis of this rare malformation.