In this chapter, the more recently identified syndrome multiple endocrine neoplasia type 4 (MEN 4) is described. The current knowledge regarding the clinical spectrum including primary hyperparathyroidism, pituitary adenomas, neuroendocrine neoplasms (NENs), and other endocrine and non-endocrine tumors is presented. Since the genetic cause is known, one paragraph focuses on genetic counseling of these patients. With regard to the treatment, particular emphasis has been put on surgical aspects.