The authors review present knowledge on multiple endocrine neoplasias types 1 and 2. They discuss in the light of recent literature data, the natural history, diagnosis, differential diagnosis and the optimal diagnostic approaches of these disorders. A short review on the therapeutic modalities draws attention to important differences between sporadic and inherited endocrine tumors. Finally, the authors emphasize recent developments about the genetic background and the importance of molecular biologic techniques, including family screening in the diagnosis of these disorders.