The case of a 33-year-old woman with bilateral partial agenesis (type D) of the posterior arch of the atlas and recurrent transient quadriparesis due to contusion of the spinal cord after minor cervical trauma is described. At least some patients with type C or D congenital anomalies of the posterior arch of the atlas are prone to transient quadriparesis; thus a more aggressive management is advocated for them. Radiological and surgical findings showing the possible causative mechanism are presented and a review of the literature is given.