The aim of this study was to ascertain whether MG7Ag is a useful predictor of evolution of gastric dysplasia to carcinoma. A total of 1090 patients with confirmed dysplasia were stained immunohistochemically with MG7 monoclonal antibody by the ABC method. A prospective follow-up study was undertaken on 19 patients with MG7Ag positive staining and 16 with MG7 negative staining over a period of 10-78 months. The expression of MG7Ag was also compared in another two groups by conducting retrospective studies. One group showed an evolution into gastric cancer over 2-4 years, the other did not. Quantitative analysis of MG7Ag expression was carried out on the last two groups. The receiver operating characteristic curve and Youden index were used to assess the best critical value for MG7Ag. MG7Ag was found positive in 456/1090 cases (41.8%) with dysplasia. Prospective follow-up of 35 patients showed that 6/19 patients with MG7Ag positive staining developed gastric cancer, but there were no carcinomatous changes in 16 patients with MG7 negative staining. The results of MG7Ag expression in 72 cases with retrospective follow-up showed there were 24 with positive immunostaining among 34 cancerous cases (70.6%), and only 7 in 38 non-cancerous cases (18.4%) (p<0.01). Image analysis showed that an average MG7Ag density index ++0.19 could be regarded as the critical value for high risk of gastric mucosa with dysplasia evolving to cancer. Positive MG7Ag expression in gastric mucosa of patients with dysplasia, especially in cases with a density index ++0.19, was an indicator of high risk of malignant change.