This review summarizes knowledge on pathology of proliferative lesions of the pituitary gland in multiple endocrine neoplasia syndrome type 1 (MENS 1). When compared with sporadic tumors occurring in general population, pituitary adenomas associated with MENS 1 show the following distinguishing features: (1) they are more often endocrinologically functional, (2) they are more often GH or PRL-producing and (3) they are more frequently plurihormonal. The study of autoptic cases discloses that pituitary PRL or mixed GH-PRL cell adenomas in MENS are multiple and are associated with PRL or GH cell hyperplasia of the peritumoral parenchyma.