The relationship between atrophic gastritis and stomach cancer risk was investigated in case-control analyses involving 387 cases with stomach cancer and 5,422 control subjects who received gastroscopic examination at Aichi Cancer Center Hospital from April, 1985 to March, 1989. The presence of atrophic gastritis, the degree and extension of the atrophy and the presence of granularity and erosion were diagnosed endoscopically by six gastroenterologists. The prevalence of atrophic gastritis increased with age and was higher in males than in females. The relative risk (RR) of stomach cancer was 5.13 (95% confidence interval (CI): 2.79-9.42) if a subject had any type of atrophic gastritis. The risk further increased with advancing degree of atrophy and increasing extension on the greater and lesser curvatures. The RR associated with severe atrophy was 7.73 (95% CI: 3.95-15.12). These associations remained significant when analyzed by sex and age. The presence of granularity and erosion did not much affect the estimated risks. A clear difference in risk appeared in the analyses by histological type of cancer. The RR associated with atrophic gastritis was 24.71 (95% CI: 3.46-176.68) for the intestinal type and 3.49 (95% CI: 1.77-6.87) for the diffuse type. These findings may suggest a need for intensive follow-up of patients with severe atrophic gastritis.