Hereditary diffuse gastric cancer is an autosomal dominant syndrome with a high lifetime risk of diffuse gastric cancer and also a high risk of lobular breast carcinoma. Hereditary diffuse gastric cancer (HDGC) is characterized by late presentation and a poor prognosis. The average age of onset of HDGC is 38 years, with a range of 14-69 years. The estimated lifetime risk of developing gastric cancer by age 80 is 67% for men and 83% for women. Many families with HDGC have germline mutations in the E-cadherin (CDH1) gene. We describe indication for genetic testing of germline mutations in CDH1 gene, possibilities of predictive testing, preventive care, prophylactic gastrectomy and preimplantation diagnosis.