The incidence of gastric cancer has declined markedly in Finland during the last 4 decades. To document the changes caused by that in the ratio of the intestinal type (IT) to the diffuse type (DT) of gastric carcinoma we compared the 367 cases diagnosed from southwestern Finland at the Department of Pathology, Turku University, from 1950-1959 and 1076 cases from 1980-1989. IT virtually disappeared in the male and female populations younger than 50 years, and in patients younger than 60 years, DT became more common than IT (P < 0.001). The transitional age, the time at which IT exceeds DT in frequency, shifted by 20 years to older age groups. In patients older than 60 years, IT remained the dominant type, but the ratio of IT to DT (IT:DT) decreased in men from 3.8 to 2.1 (P < 0.05) and in women from 4.4 to 2.1 (P < 0.001). No decrease in the frequency of DT could be demonstrated in the material studied. The disappearance of the male-dominant IT in the younger male population changed the male-to-female ratio of patients reported to the Finnish Cancer Registry. When the ratio IT:DT in Finland was compared with the ratios reported by the authors in data from other continents and by other investigators, regional variations in basal level of IT:DT emerged. This phenomenon seems to be based on the differing genetic susceptibility to DT of various races. The decrease of IT, seen in reports from regions with declining incidence of gastric carcinoma, seems to be connected to a diminished rate of severe chronic gastritis.