BACKGROUND: Most gastric cancer (GC) is sporadic and seem to be mostly related to a cumulative effect of multiple environmental factors. Although the actual importance of genetic factors has not yet been fully documented, GC with familial aggregation has been found to have an incidence of 10% to 30%. MATERIALS AND METHODS: Genetic factors contribute to the well-known autosomal dominant syndrome defined as hereditary diffuse gastric cancer (HDGC) which can be related to germline mutations of the gene encoding E-cadherin gene (CDH1). It has been estimated that 1-3% of cases of GC are due to HDGC. DISCUSSION AND CONCLUSION: The authors review data on CDH1 mutations in HDGC ,CDH1 testing criteria, and treatment. They conclude that cancer pedigrees and screening for CDH1 mutations are essential for improving the management of this disease.