Between January 1981 and December 1985 at the Rizzoli Orthopaedic Institute 8 patients affected with atlo-axial instability secondary to os odontoideum were submitted to surgery: all of the patients were characterized by persistent cervical pain and neurological deficit, which was still at an initial stage in 5 cases, and more severe in the remaining 3 (severe spastic tetraparesis). All of the patients were submitted to a similar treatment protocol in three stages: 1) preoperative reduction in halo-plaster, 2) surgical stabilization of C1-C2 by posterior vertebral fusion (limited to C1-C2 in 6 cases and extended as far as the occiput in the remaining 2), 3) postoperative immobilization in halo-plaster for an average of 12 weeks. At follow-up obtained after an average of 4 years and 2 months there was consolidation of the fusion in all of the cases treated: in 1 case, however, revision of the fusion was required 3 and 1/2 months after surgery, whereupon fusion was finally obtained. The total regression of pain was obtained in all 8 of the cases treated and there was evident neurological recovery in the 3 patients who had been characterized by severe spastic tetraparesis prior to surgery. The treatment protocol used in this series of patients proved to be a reliable one. Thus, it was possible to avoid the onset of chronic atlo-axial instability and its severe neurological sequelae in those cases where neurological deficit was still at an initial stage; furthermore, effective recovery was obtained in patients in whom neurological deficit was severe.