The E-cadherin mutation has been identified in a subset of families with multiple cases of diffuse gastric carcinoma. However, the true penetrance of this mutation and its association with other carcinomas in such families remains elusive. We aim to show the importance of DNA-based genetic counseling in hereditary diffuse gastric carcinoma. The proband was self-referred after three of his siblings died of diffuse gastric carcinoma. Medical and pathology records confirmed diagnoses. The family was educated about diffuse gastric carcinoma. Analysis for the 70G-->T mutation was performed by sequencing genomic DNA from lymphocyte pellets. DNA results and genetic counseling were provided individually to those tested. Twenty-four family members were tested for the E-cadherin mutation. Nine were found to be positive and 15 were negative. Three who tested positive and were affected are now deceased. None of the 19 patients counseled wanted results sent to their physicians once they recognized the potential for insurance discrimination. None had undergone endoscopic ultrasound. Three who were positive for the E-cadherin mutation expressed strong interest in prophylactic gastrectomy. The E-cadherin mutation strongly predicts susceptibility to diffuse gastric carcinoma. Emotional stress in at-risk patients, the limited knowledge of the mutation's penetrance, and limitations of available screening mandate patient-centered genetic counseling.