AIM: To eluddate the relations between the myeloperoxidase -468G→A polymorphism and the development of duodenal ulcer (DU), and to investigate the impacts of this host genetic polymorphism on the histopathological featuresof Helicobacter pylori ( H pylori)-related gastritis. METHODS: In a case-control study of 115 consecutive DU patients and 182 controls, the myeloperoxidase-468G→A polymorphism was genotyped. Additionally, gastric mucosal changes were examined according to the updated Sydney System.RESULTS: The two study groups differed in the distributionsof myelperoxidase genotypes (P= 0.008). All six individuals carrying myeloperoxidase A/A genotypes were in the DU group. The carriage of myeloperoxidase allele A and H pylori infection were associated with an increased risk of DU with odds ratios (OR) of 2.3 and 5.8, respectively. Thecombined risk of the carriage of myeloperoxidase allele A and H pylori infection for DU was 8.7 (95% CI, 3.5-21.8). In the H pylori-infected individuals, allele A carriers displayed higher bacterial density scores (P = 0.04) inthe antrum than did non-carriers.CONCLUSION: This work verifies for the first time the association of myeloperoxidase-468G→A polymorphism with antral H pyloridensity and DU disease. The mechanisms underlying this genetic polymorphism in developing DU disease merit further investigations.