Epidemiological data show an association between Helicobacter pylori gastritis and gastric carcinoma. However, most people infected with H. pylori do not develop gastric cancer. We have therefore evaluated histological criteria indicating an increased risk for gastric cancer. H. pylori gastritis was investigated in 117 patients with small (O<2 cm) early gastric carcinomas and in 117 age-matched duodenal ulcer patients infected with H. pylori, who are known to have a low risk for developing gastric carcinoma. The results showed that infiltration with lymphocytes/plasma cells and infiltration with neutrophils predominating in the corpus, and intestinal metaplasia in antrum and corpus were associated with both types of gastric carcinoma (intestinal and diffuse, P<0.0001). If an index is computed by giving one point to each of these features, the predictive value for the presence of gastric carcinoma was 0.79 with a score of 2, and 0.94 with a score of 3 (all points on the index used). Application of this index might be a simple method of identifying patients infected with H. pylori and carrying a higher risk for gastric carcinoma.