The prevalence of Helicobacter pylori infection is high among Asian populations, but the incidences of gastric cancer differ greatly among northern and southern Asian populations. Here, we studied histopathological findings in stomach tissue using an updated Sydney System and the frequencies of interleukin (IL)-1betapolymorphisms, thought to be associated with an increased risk of gastric cancer, in four Asian populations. Endoscopic-guided biopsies from three regions of the stomach and the -511 T-to-C polymorphism in the IL-1betagene were examined in 228 Japanese, 116 Chinese, 159 Thai and 83 Vietnamese patients with gastric diseases. H. pylori colonization, inflammation and activity were more severe in the Japanese and Thai populations than in the Chinese and Vietnamese populations and these scores were more antrum-predominant in the Thai and Vietnamese populations than in the Japanese and Chinese populations, with the most severe degree of atrophy and intestinal metaplasia occurring in the angulus region of the Japanese population. The IL-1betapolymorphisms did not differ among the four populations overall, but in cases with severe mucosal atrophy (pepsinogen I/II ratio <3.0), the CC polymorphism was dominant in the Japanese population and the TT+TC polymorphism was dominant in the Chinese population; no difference in C and T allele frequencies was found in the Thai and Vietnamese populations. In conclusion, the incidence of gastric cancer is extremely low, but the prevalence of H. pylori infection is high in the Thai population (Asian paradox). In the Thai population, the scores for corpus gastritis and intestinal metaplasia, which are associated with a high risk of gastric cancer, were low in comparison with the Japanese population. IL-1betapolymorphisms were correlated with mucosal atrophy in the Japanese and Chinese populations, but not in the Thai and Vietnamese populations.