Objective To investigate the clinical values of the expression of proliferating cell nuclear antigen(PCNA) and S-100 in the ossified mass of the cervical posterior longitudinal ligament.Methods The 22 pieces of ossified mass specimens of the cervical posterior longitudinal ligament were obtained from 22 patients with ossification of posterior longitudinal ligament(OPLL) by anterior decompression approach in the cervical spine.Of the 22 specimens,3 specimens were obtained from the patients after laminoplasty.As controls,5 specimens of the cervical posterior longitudinal ligament were obtained from 5 fresh corpses below 25 years old by anterior approach.All the specimens were stained with HE and immunohistochemically stained with the monoclone antibody against the PCNA and the monoclone antibody against the S-100 protein antigen. Results The PCNA and S-100 were overexpressed in the ossifing matrices and chondrocytes of adjacent cartilaginous areas of ossification of the posterior longitudinal ligament.There was no expression of PCNA and S-100 in the controlled specimens.Conclusion The ossified mass of the cervical posterior longitudinal ligament has a character of continuous proliferation and ossification.The proliferating fibrocartilaginous areas before the ossified mass is an important pathogenetic factor of cervical myelopthy recurrence after laminoplasty.