Objective To provide appropriate guidelines for treatment of tandem ossification of the posterior longitudinal ligament (OPLL) and flaval ligament (OFL). Data sources Published articles about OPLL and OFL were selected using Medline and Embase electronic databases. Study selection An English literature search from January 1980 to December 2006 was conducted. Because many reported cases were incorporated in OFL studies, the key words for search were OFL or OFL and OPLL. The first step revealed 93 studies of which 13 reports of tandem OPLL and OFL (tandem ossification) were selected. Results All studies were case series or case report and advocated that the primary therapy for tandem ossification should be operative. The clinical outcomes of surgery were evaluated in most reports, predominantly using the JOA scores. Gender is the only factor which has prognostic value. A higher proportion of women was found in the failure group. A two- stage classification of tandem ossification was developed to relate diagnosis to outcome. Conclusions All patientS with suspected ossification of the spinal ligaments should undergo routine MRI screening of the whole spine. The correlation of the classification with surgical treatments needs further studies to validate its usefulness.