Gastric cancer remains a great clinical challenge despite its decreasing incidence. While major progress has been achieved in the understanding of the pathogenesis and molecular biology of sporadic gastric cancer, only recently has the role of familial aggregation of gastric cancers been rediscovered. The genetic changes underlying sporadic and familial gastric cancer have been revealed, and recent studies indicate that this familial aggregation combines genetic and microbiological aspects. Thus, for the prevention of gastric cancers these findings might be helpful for the early diagnosis and for the screening of risk groups and family members.