Plurihormonal adenomas of the pituitary, ie, tumors that engage in the production of unusual combinations of hormones, represent approximately 10% to 15% of all adenomas. Such tumors comprise in excess of 50% of adenomas in the setting of acromegaly and occur with somewhat greater frequency in childhood and adolescence than in adulthood. Eight percent are associated with multiple endocrine neoplasia, type I. The most common variant of plurihormonal adenoma produces growth hormone, prolactin, and one or more glycoprotein hormones, the most common being TSH. Clinical effects most often reflect the presence of growth hormone, and to a lesser extent, prolactin cells; expression of glycoprotein hormone production is rare. The tumors are more often macroadenomas (80%) than microadenomas (20%) and demonstrate gross invasion in 50% of cases. Plurihormonal adenomas may be ultrastructurally monomorphous, bimorphous, or trimorphous; thus, one morphologic cell type may elaborate several hormones.