Hereditary diffuse gastric cancers are rare, accounting for at most 1-3% of gastric cancers. It can be caused by a mutation in the tumour-suppressor gene CDH1. A healthy person carrying a CDH1 mutation has a cumulative risk of developing gastric cancer of 70-80%. In most cases, gastric cancer is detected before the age of 40 years. The effectiveness of screening for hereditary diffuse gastric cancer or early detection with twice-yearly upper GI endoscopy with blind biopsies is highly questionable. Given the poor prognosis of patients with hereditary diffuse gastric cancer, prophylactic gastrectomy can be considered an option for patients with a CDH1 mutation. It is recommended that the supervision, screening and possible preventative gastrectomy for hereditary diffuse gastric cancers are handled by a multidisciplinary team in a specialised centre.