The rapid growth of molecular genetics and its attendant germline mutation discoveries has enabled identification of persons who are at an inordinately high cancer risk and, therefore, ideal candidates for prevention. However, one must fully appreciate the extensive genotypic and phenotypic heterogeneity that exists in hereditary cancer. Once the causative germline mutation has been identified in a patient, high-risk members of the family can be similarly tested and identified and provided highly targeted surveillance and management opportunities. DNA testing can change the individual's presumed risk status and affect decision making by patients and their physicians regarding surveillance and management. Our purpose is to describe familial/hereditary cancers of the gastrointestinal tract, including familial Barrett's esophagus, hereditary diffuse gastric cancer, gastrointestinal stromal tumors, familial adenomatous polyposis and desmoid tumors, Lynch syndrome, small bowel cancer, and familial pancreatic cancer. We use our discussion of Lynch syndrome as a model for diagnostic and clinical translation strategies for all hereditary gastrointestinal tract cancers, which clearly can then be extended to cancer of all anatomic sites. Highly pertinent questions from the patient's perspective include the following: What kind of counseling will be provided to a patient with a Lynch syndrome mutation, and should that counseling be mandatory? Does the proband have the responsibility to inform relatives about the familial mutation, even if the relatives do not want to know whether they carry it? Is the patient is responsible for notifying family members that a parent or sibling has Lynch syndrome? Can notification be forced and, if so, under what circumstances? These questions point out the need for criteria regarding which family members to inform and how to inform them.