To investigate the association between the promoter polymorphism -509C/T of the transforming growth factor-β1 gene (TGFB1) and the disease severity of allergic rhinitis (AR) in childhood.A total of 96 Chinese patients with persistent AR aged 3 - 17 (9.4 ± 3.8) years old were enrolled in the study. Among these patients 53.1% were mild cases (n = 51) and 46.9% were moderate-to-severe cases (n = 45). Genotyping was performed on peripheral blood genomic DNA by using PCR-RFLP. Serum levels of TGF-β1 was measured by ELISA, and serum total IgE, specific IgE and eosinophil cationic protein (ECP) levels were determined using an ImmunoCAP100E system. Statistical analysis was conducted with SPSS11.0 software.Significant differences were found in genotype frequencies for the TGFB1-509C/T polymorphism between mild and moderate-to-severe AR patients (χ(2) = 8.361, P = 0.015). Children with persistent AR bearing the TT genotype of the -509C/T polymorphism had significantly increased risk for moderate-to-severe AR (Fisher's exact test, P = 0.007) compared to children with the CC/CT genotypes. There was no significant association between the -509C/T polymorphism and serum TGF-β1 levels (F = 0.389, P = 0.679); however, serum total IgE (F = 4.210, P = 0.018) and ECP (H = 6.297, P = 0.043) levels were found to be significantly associated with the polymorphism.The results suggest that the TGFB1 gene polymorphism -509C/T may play a potential role in the severity of persistent AR in childhood.