The purpose of this study was to examine whether patients with gastric cancer differ from those with benign gastroduodenal diseases in terms of familial disposition. This series consisted of 1,233 patients with gastric cancer and 2,200 patients with benign gastroduodenal diseases, who had had a gastrectomy between 1972 and 1979 in one hospital. The family information on cancer deaths of first and second relatives of the patients was obtained at the time of operation. The age-adjusted relative risk of positive family history of cancer was higher among the patients with gastric cancer than that among those with benign gastroduodenal diseases. The patients with diffuse type of cancer had a higher risk of positive family history than those with intestinal type of cancer. The non-cancer patients with family history had a slightly higher risk, although not statistical significant, to die from cancer than those without family history. Higher frequency of blood type A was seen in gastric cancer patients with positive family history. These results suggest that certain types of gastric cancer may seem to be associated with genetic factor.