Background: It has been recognised that genetic or hereditary factors may contribute to the aetiology of adolescent idiopathic scoliosis (AIS).Recently, two linkage analyses have identified 19p13.3 as the candidate region for AIS.The dipeptidyl peptidase 9 (DPP9) gene is located on chromosome 19p13.3.Objective: To investigate whether DPP9 gene polymorphisms are associated with the occurrence or curve severity of AIS.Methods: 571 girls with AIS and 236 normal controls were recruited.Using the Chinese data from the HapMap project, a set of tagging single-nucleotide polymorphisms (tagSNPs) were defined for the DPP9 gene.Five SNPs were genotyped by PCR restriction fragment length polymorphism.Statistical analysis of genotype frequencies between cases and controls was performed by the X2 test.One-way analysis of variance was used to compare mean maximum Cobb angles with different genotypes in case-only analysis.Besults: Genotype frequencies were comparable between cases and controls for all five polymorphisms (p>0.05).The mean maximum Cobb angles of different genotypes were similar to each other for all five polymorphisms.Conclusions: The DPP9 gene is not associated with the occurrence or curve severity of AIS.It is neither a disease-predisposition nor a disease-modifying gene of AIS.