In Japan, there have been a few reports on the familiar factors of gastric cancer (GC) and on the GC risk related to family history (FH) at other cancer sites. We analyzed the association between GC occurrence and a positive FH of cancer of the stomach and of other sites in a hospital-based case-control study. The subjects included cases histologically confirmed as incident cancer of the stomach (n = 136; 86 male and 50 female patients) and sex and age (+/- 1 year)-matched controls. GC risk was high when a subject had a parental history of GC [Mantel-Haenszel odds ratio adjusted for sex and age (OR)=2.3; 95% confidence interval (95% CI):1.1-5.0]. GC risk was almost unity for a cancer FH of any other cancer site, even among closer relatives, suggesting little or no contribution to GC occurrence. The familial occurrence of GC found in this study suggests the existence of a genetic susceptibility to cancer of the stomach. Further, females tended to show higher GC risks than males, when reporting an affected mother (OR=6.0; 95% CI:1.1-31.4 and OR= 1.4; 95% CI:0.4-4.8, respectively), whereas males showed a slightly higher risk than females when reporting an affected father (OR=2.4; 95% CI:0.8-7.5 and OR=2.3; 95% CI:0.4-15.6, respectively). This suggests a possible gender difference in how environmental factors influence GC occurrence. The development of gastric tumors seems to be due to a complex and unknown interaction between environmental and genetic factors.