This study attempts to determine the relative prevalence of intestinal-type and diffuse-type carcinomas (using a modified Lauren classification of gastric carcinomas) and to evaluate its significance in relation to the difference in stomach cancer risks among the different ethnic and Chinese dialect groups in Singapore. Of the 648 cases of primary adenocarcinoma of the stomach studied, 405 (62.5%) were of the intestinal type, 206 (31.8%) of the diffuse type, and 37 (5.7%) of the mixed type. Men had higher proportions of intestinal-type carcinoma than women. The intestinal-diffuse carcinoma ratio increased progressively with age. Although the relative intestinal-diffuse carcinoma ratios in women appeared to reflect the relative incidence rates of stomach cancer of the different ethnic and dialect groups, the ratios in men were inconsistent. Indian men had a higher intestinal-diffuse carcinoma ratio than Chinese men despite a lower incidence of stomach cancer. Hokkien men had the highest incidence of stomach cancer and the lowest intestinal-diffuse carcinoma ratio among the Chinese dialect groups. The use of the ratio as an indicator of relative risks for gastric cancer between populations of different genetic makeup is inconsistent and unreliable.