Psoriasis is one of the most common inflammatory diseases of skin. MCP-1 is an important CC-type chemokine responsible for monocytes and T lymphocytes recruitment in inflammatory conditions. A single nucleotide polymorphism of the MCP-1 gene in the gene regulatory region was found to be related to the expression of MCP-1, and the associations of this polymorphism with many inflammatory diseases were conformed. However, the significance of this polymorphism in psoriasis remains unclear. Therefore, we examined this polymorphism in 507 patients with plaque-type psoriasis and 530 healthy controls using the polymerase chain reaction-restriction fragment length polymorphism method. We also tested the serum MCP-1 in 320 patients and 160 controls and compared the serum MCP-1 level in patients of different genotypes. Our results showed that the frequency distribution of the AA, AG and GG genotypes between the patients and the controls was statistically different (P = 0.031); significantly increased risk for psoriasis was associated with the AG, GG and AG + GG genotype. The frequency distribution of the AA, AG and GG genotypes was also different between female psoriasis patients and controls (P = 0.025), between type I psoriasis patients and controls (P = 0.025), between psoriasis patients without positive familial history and controls (P = 0.048), and between patients with psoriasis area and severity index of > or = 10 and controls (P = 0.041). MCP-1 serum level was significantly higher in patients than controls (P < 0.0001). There were significant differences of serum MCP-1 level between patients of the GG genotype and the AA genotype (P = 0.028), between patients of the AG genotype and the AA genotype (P = 0.049), and between patients of the AG + GG genotype and the AA genotype (P = 0.027). These results showed the -2518 MCP-1 polymorphism is related to the susceptibility of plaque type psoriasis. Individuals containing the GG or AG genotype were at higher risk of psoriasis than subjects with the AA genotype.