Objective: To report a case of cervical instability caused by craniocervical malformation with ossification of the posterior longitudinal ligament (OPLL) treated by anterior controllable antedisplacement and fusion (ACAF). Methods: A 70 years old male patient was admitted to our hospital due to a year of numbness in the trunk and both arms, which was exacerbated over the past 2 months with unsteady gait. He was diagnosed with cervical spondylotic myelopathy with incomplete paralysis, craniocervical malformation due to atlantooccipital fusion and absence of odontoid process, and OPLL. C2-4 disectomy was performed on the patient, and appropriately sized intervertebral fusion cages filled with artificial and autogenous bones were inserted into the C2/3 and C3/4 intervertebral space. Bones at the anterior margin of the vertebrae were thinned based on the thickness of ossification at each involved segment, and titanium plates were installed at the anterior margin of C2-4. Bilateral osteotomies of C3 were performed using an ultrasonic bone curette, and residual cortical bones at the posterior margin of the vertebrae were removed using a 1 mm bayonet rongeur, along with enlargement of the nerve root canal at the corresponding segment. Upon verification of nerve root canal patency, C3 screws were tightened to achieve antedisplacement. Results: Postoperative MRI showed complete decompression of the cervical cord after isolation and antedisplacement of the vertebrae-ossification complex by ACAF. Japanese Orthopaedic Association (JOA) score of patient was improved from 6 to 10 at 3d post-surgery. Conclusion: ACAF is a surgical method that combines the effectiveness of direct decompression by the anterior approach with the safety of indirect decompression by the posterior approach. Its good biomechanical properties, ability to achieve complete decompression and low risk of surgical complication make ACAF a promising treatment for OPLL with cervical instability.