Nine of twelve family members from three generations were affected by an inherited form of cervical vertebral dysplasia. All of the affected people had an abnormality of the first cervical vertebra. Some also had defects of the axis and caudad to it. The mode of transmission of the disorder is autosomal dominant, with apparently complete penetrance and variable expressivity. Two patients had symptoms. One had a passively correctable tilt of the head, with an associated audible clunk and hypoplasia of the left superior facet of the second cervical vertebra. This patient had no local symptoms, neurological involvement, or muscle spasm. In the other patient, suboccipital pain developed. Radiographs revealed an anterior atlanto-occipital dislocation. The symptoms resolved after reduction and arthrodesis. Because of the apparently complete penetrance of this disorder, physicians caring for patients who have this type of congenital malformation of the cervical spine should consider examination of closely related members of the family. Clinical findings such as tilting of the head, torticollis, or limitation of cervical motion suggest that additional evaluation should be done. The examination should include lateral radiographs of the cervical spine in flexion and extension. Three-dimensional computed-tomography reformatting was helpful in demonstrating the complex cervical anatomy in our patients. Patients who have recognized abnormalities should be followed and should be re-examined whenever local or neurological symptoms develop. A magnetic resonance image of the spine in flexion and extension was valuable for identification of the potentially disastrous situation of impending damage to the cord in patients who had instability and evolving symptoms.