Ossification of the posterior longitudinal ligament (OPLL) is a condition of the spine that can cause paralysis by compressing the spinal cord. The aim of this study was to evaluate the possible role of nucleotide pyrophosphatase phosphodiesterase 1 gene (NPP1) polymorphism in the etiology and pathology of the OPLL in Chinese patients. DNA from patients with OPLL (N = 95) and without OPLL (N = 90) were genotyped for 4 NPP1 single-nucleotide polymorphisms (SNPs): A533C, C973T, IVS15-14T→C, and IVS20-11delT. An association study evaluated the relationship between specific SNP genotypes and susceptibility. We also evaluated whether genotypes of these SNPs were associated with disease severity and the probability of disease progression after surgery. The C973T and IVS15-14T SNPs were associated with the existence of the disease. The TT genotypes of C973T and IVS15→14T as well wild-type IVS20 (lack of deletion) were associated with more severe disease. Patients with the Tdeletion of IVS20 or the AA genotype of A533C had an approximately 3 times greater chance of not having than having disease progression after surgery. We concluded that the 4 SNPs analyzed appeared to have different effects on the etiology and pathology of OPLL. To our knowledge, this study is the first to investigate the relationship between these SNPs and disease progression after surgery. Our findings suggest that the presence of specific genotypes of the IVS20-11delT and A533C SNPs may predict disease outcome after surgical intervention.