Background Several candidate genes of ossification of the posterior longitudinal ligament (OPLL) susceptibility have been identified, but their polymorphisms account for only a small percent of the total variance. Bone morphogenetic protein-4 (BMP4) is a potent ectopic ossification inducing factor. BMP4 protein and mRNA are present in cells from OPLL patients, but not non-OPLL controls. A single nucleotide polymorphism of 6007C>T(rs17563) of BMP4 has been reported to affect bone density in postmenopausal women. Thus, BMP4 may function in OPLL development. Appropriately, the relationship between BMP4 polymorphisms and OPLL was investigated.Methods A case-control association study investigated the genetic etiology in 179 OPLL patients and 298 non-OPLL controls. Extent of OPLL was analyzed by radiologic examinations. Whether single nucleotide polymorphism (SNP) of -5826G>A(rs1957860) 5′ of the transcription start site and 6007C>T(rs17563) in exon 4 of the BMP4 gene were statistically associated with genetic susceptibility to OPLL in Chinese Han subjects was assessed.Results A significant statistical difference in genotype of 6007C>T polymorphism between male OPLL patients and male controls was evident, and the frequency of "TT" genotype in male OPLL patients was significantly higher than in male controls (P=0.039). The frequency of the "T" allele was also significantly higher in male OPLL subjects than in male controls (P=0.014, 0R=1.57). A significant difference was also observed between the 6007C>T polymorphism and the number of ossified cervical vertebrae in OPLL patients, while no statistical difference was apparent between the -5826G>A polymorphism and OPLL occurrence.Conclusions The T allele in the 6007C>T polymorphism may be a risk factor for male Han Chinese with ossification of the posterior longitudinal ligament in the cervical spine. Chinese Han male patients with CT and TT 6007C>T genotypes have a genetic susceptibility to OPLL and more extensive OPLL in the cervical spine.