The history of stomach cancer epidemiology is reviewed. The introduction of migrant population studies in the 1960 decade that described the critical role of exposures to this disease in early life was a key event. Companion pathology studies have indicated different epidemiological patterns for 2 histological entities, intestinal and diffuse type carcinomas, and confirmed an excess of intestinal metaplasia in populations at high risk to stomach cancer. Recent results suggest that epidemiology of stomach cancer can be transformed into the epidemiology of precursor lesions, and introduction of the fiberoptic gastroscope makes technically feasible detailed studies of the relationship of precursor lesions to suspect factors, including diet, in selected geographic areas. Nitroso compounds have been identified as candidate carcinogens and the epidemiological, pathological, and chemical data display signs of internal consistency. Feeding experiments with N-methyl-N′-nitro-N-nitrosoguanidine have led to animal models that permit a coordinated epidemiological-experimental approach to stomach cancer.