Neither the natural history nor the optimal treatment of cervical spine anomalies in Larsen's syndrome has been clearly defined. The authors describe two patients with Larsen's syndrome with cervical kyphosis, anteroposterior dissociation, and quadriparesis to show the variable clinical progression and offer a description of the authors' treatment. One patient has had continued neurologic and radiographic improvement with nonoperative treatment consisting of early traction. The other patient was treated with posterior fusion that failed to halt progressive kyphosis of the anterior vertebral bodies because of anteroposterior dissociation. He then was treated by resection of the posterior fusion, traction, and anterior and posterior decompression and fusion. Cervical kyphosis in patients with Larsen's syndrome is unpredictable, and both nonoperative and operative treatments have the potential to be successful. Anteroposterior dissociation of the cervical spine may be more common in Larsen's syndrome than recognized previously and may profoundly affect operative strategy and outcome.