Multiple endocrine neoplasia type 1 (MEN1) is a rare autosomal dominant hereditary tumor syndrome with a high degree of penetrance, that is caused by inactivating mutations of the tumor suppressor gene MEN1, and is characterized by a predisposition to a multitude of endocrine and nonendocrine tumors (1). The gene discussed is MEN1; the disease is multiple endocrine neoplasia type 1.