Chronic atrophic gastritis is regarded as a predisposing factor for gastric cancer associated with Helicobacter pylori infection, and its severity is suggested to be a key influence on gastric cancer risk. Our purpose was to elucidate chronological change in cumulative risk of gastric cancer occurrence with various degrees of chronic atrophic gastritis by long-term follow-up. A total of 5373 subjects without cancer or resected stomachs who underwent gastroscopic examination and completed a life-style questionnaire between 1985-1989 were prospectively followed until December 1999. Relative risks of gastric cancer associated with baseline endoscopic findings were estimated using hazard ratios and their 95% confidence intervals with the Cox proportional hazard model, adjusting for gender, age and gastric cancer family history. After an average of 10 years of follow-up, 117 gastric cancer cases were identified. The risk was greatest among the subjects with moderate atrophy at baseline (hazard ratio: 2.22) and 4-6 years of follow-up (hazard ratio: 4.6-5.0). After this time point, risk attenuation with the length of follow-up period was observed. Our study gives the supportive evidence to the hypothesis that incomplete chronic atrophic gastritis and the processes occurring in atrophy are associated with development of gastric cancer.