Abstract: Objective To investigate the association of interleukin-1A-889 gene polymorphisms and smoking with the susceptibility to chronic periodontitis in Han nationality.Methods 142 chronic periodontitis(CP)patients and 95 healthy controls were selected and the information of whether or not smoking was obtained through questionnaire survey;DNA was extracted from these buccal swabs and genotypes of the IL-1A-889/NcoⅠwere determined by sequence specific primers polymerase chain reaction(SSP-PCR)and PCR restriction fragment length polymorphism(PCR-RFLP).Then the interaction between the genotypes of L-1A-889/NcoⅠand smoking was analysed.Results There were 46 severe chronic periodontitis(CP)patients,45 moderate CP patients and 51 mild CP patients in 142 chronic periodontitis(CP)patients.Frequencies of allele 2 for IL-1A-889/NcoⅠwere higher in severe CP patients than in healthy controls,and the difference was statistically significant(P<0.01).But there were no such significant differences either between moderate CP patients and healthy controls or between mild CP patients and healthy controls.Smoking can significantly increase the incidence of periodontal disease,and there were interaction between the genotypes containing allele 2 and smoking(OR=10.413,P=0.000;OR=5.315,P=0.004).Conclusion IL-1A-889 may be a risk indicator for the susceptibility to severe chronic periodontitis in Han nationality,and smoking was associated with CP and may represent a risk factor for this disease.Individuals carrying the positive genotype have significant risk for CP.