The role of gastric epithelial dysplasia (GED) as a biological and morphological precursor of gastric cancer has been widely investigated, but few studies have prospectively evaluated the risk of its evolution into gastric cancer. In 1985, a prospective multicenter follow-up study was undertaken on patients with high-grade (moderate or severe) GED. The study involved 49 patients, with a follow-up currently averaging 18.8 months (range: 1-70) and a mean number of 4 endoscopies (range: 2-10). Follow-up was abandoned when 2 subsequent control endoscopies and a 1-year period were negative for GED, or when neoplasia was detected. Gastric cancer was diagnosed in 16 cases (33%). The cancer was detected at an early stage in 10 patients (62%). Eleven cases (59%) were diagnosed within 1 year of follow-up and 5 cases after 13, 18, 21, 24 and 39 months, respectively. Cancer was associated with 36% of moderate GED cases and with 80% of severe cases. Dysplastic changes were no longer detectable at follow-up in 27% of the moderate cases and in 10% of the severe cases. The relative risks for the two lesions being associated with or evolving into gastric cancer were 26 and 132, respectively. In conclusion, high-grade (moderate or severe) GED is frequently associated with or evolves into gastric cancer. The follow-up of patients considerably enhances the chances of diagnosing gastric cancer in its early stages, thus making such an approach mandatory.