Multiple endocrine neoplasia type 1 (MEN1) is characterized by the combined occurrence of primary hyperparathyroidism, pancreatic endocrine tumors, and neoplasms of the anterior pituitary gland. The disease is inherited as an autosomal dominant disorder with a high penetrance. Although many investigators have localized the causative genes to chromosome 11q3 by linkage analysis, the MEN1 gene remains unidentified. The use of molecular genetic markers in family linkage studies, however, have made it possible to identify gene carriers. Repetitive screening combined with the assignment of gene-carrier status will provide possibilities for therapeutic or prophylactic intervention earlier in the development of each of the manifestations of this syndrome, such as gastrointestinal bleeding secondary to ulcers or malignant transformation.