AIM:To study the association between Interleukin-1 (IL-1) and tumor necrosis factor (TNF)-α polymorphisms, infection by Helicobacter pylori ( H pylori) and the development of gastrointestinal diseases. METHODS:Genomic DNA was ext racted f rom the peripheral blood of 177 patients with various gastrointestinal diseases and from 100 healthy volunteers. The polymorphisms in IL-1β and TNF-α genes were analyzed using the polymerase chain reactionrestriction fragment length polymorphism method PCRRFLP) and those from IL-1RN with PCR. The presence of infection due to H pylori and the presence of the CagA toxin were detected by serology. The histopathological parameters in the gastric biopsies of the patients were according to the Sydney classification. RESULTS:A comparison of the frequencies of the different polymorphisms studied among the patients and the control group demonstrated that the allele IL- 1RN*2 was more frequent among patients with gastric ulcers and adenocarcinoma. Carriers of the allele ILRN* 2 and those with reactive serology for anti-CagA IgG had a greater risk of developing peptic ulcer and gastric adenocarcinoma, as well as a higher degree of inflammation and neutrophilic activity in the gastric mucosa. CONCLUSION:Our results indicate a positive association between IL-1RN gene polymorphism and infection by positive H pylori CagA strains and the development of gastric ulcers and adenocarcinoma.