Atlanto-axial instability is an important condition that may threaten the integrity of spinal cord, leading to tetraplegia or sudden death. Many of these require operative stability, and several different operations have been advocated. Among these methods, Brooks and Jenkins posterior fusion for eleven cases of atlanto-axial instability (fresh fracture of odontoid process in nine, nonunion of odentoid fracture in one, Cl-2 rotary subluxation in one) was performed in Baik Hospital from July 1978 to June 1987, and the following results were obtained. l. Accurate reduction and immediate rigid stability were obtained with Brooks and Jenkins posterior fusion, so early ambulation with simple external support was begun within 2 weeks after operation. 2. Radiological fusion of atlanto-axial instability were seen in average 12 weeks after operation. Therefore posterior atlanto-axial fusion by Brooks and Jenkins method is an excellent method for operative treatment of atlanto-axial instability.