The diagnosis of MEN1 is established if the patient has at least two of the classical manifestations of this syndrome (PHPT, a pituitary adenoma or NENs of gastro-entero-pancreatic tissue; clinical criteria) or at least one MEN1-related tumor and a first-degree relative with genetically confirmed MEN1 (familial criteria), or finally the pathologic mutation in the MEN1 gene in the index case (genetic criteria). The gene discussed is MEN1; the disease is neoplasm.