AIM： To investigate the occurrence of chromosome 3, 7, 8, 9, and 17 aneuploidies, TPS3 gene deletion and p53 protein expression in chronic gastritis, atrophic gastritis and gastric ulcer, and their association with H pylori infection. METHODS： Gastric biopsies from normal mucosa （NM, n = 10）, chronic gastritis （CG, n = 38）, atrophic gastritis （CAG, n=13） and gastric ulcer （GU, n=21） were studied using fluorescence in situ hybridization （FISH） and immunohistochemical assay. A modified Giemsa staining technique and PCR were used to detect Hpylori. An association of the gastric pathologies and aneuploidies with Hpylori infection was assessed. RESULTS： Aneuploidies were increasingly found from CG （21%） to CAG （31%） and to GU （62%）, involving mainly monosomy and trisomy 7, trisomies 7 and 8, and trisomies 7, 8 and 17, respectively. A significant association was found between H pylori infection and aneuploidies in CAG （P=0.0143） and GU （P=0.0498）. No TP53 deletion was found in these gastric lesions, but p53-positive immunoreactivity was detected in 45% （5/11） and 12% （2/17） of CG and GU cases, respectively. However, there was no significant association between p53 expression and H pylori infection. CONCLUSION： The occurrence of aneuploidies in benign lesions evidences chromosomal instability in early stages of gastric carcinogenesis associated with Hpylori infection, which may confer proliferative advantage. The increase of p53 protein expression in CG and GU may be due to overproduction of the wild-type protein related to an inflammatory response in mucosa.