Familial neuroendocrine tumors are reviewed. The most dramatic advances have been the application of molecular genetic techniques to define the etiologies and develop predictive testing for patients with multiple endocrine neoplasia type 1 and type 2 syndromes. All three neoplastic lesions involved in multiple endocrine neoplasia type 1 (parathyroid, pituitary, and pancreatic islet) have shown loss of heterozygosity at chromosome 11. By contrast, the most consistent occurrence of loss of heterozygosity in tumors from multiple endocrine neoplasia type 2 patients was not at chromosome 10 but at chromosome 1 p. Molecular genetic testing of multiple endocrine neoplasia type 1 and type 2 family members at risk provides a powerful tool for early identification and treatment of susceptible individuals. Efforts to clarify familial neuroendocrine tumors without associated multiple endocrine neoplasia syndromes continue. The best characterized tumor of this type is familial medullary thyroid carcinoma. Familial paraganglioma, neuroblastoma, and carcinoid also are reviewed. Potential barriers to genetic screening for familial neuroendocrine tumors are discussed.