The large majority of neoplasms located in the sella turcica are benign pituitary adenomas derived from cells of the adenohypophysis. Pituitary adenomas represent the third most common primary intracranial tumor in neurosurgical practice, outnumbered only by gliomas and meningiomas. Their biology of pituitary adenomas is complex and they can cause a variety of endocrine syndromes and disorders, based on hormone profile secreted by proliferating cells. The aim of this study was to evaluate the routine conventional methods and highly specific immunohistochemical methods in order to accurately predict the type of hormone secretion. Our study was investigated 142 cases admitted with pituitary adenomas and treated by open surgery. Sections from each case were stained with routine Hematoxylin and Eosin method for histopathologic evaluation. Immunohistochemistry was performed on additional slides in order to detect specific pituitary adenomas. Based on the immunohistochemical profile of pituitary adenomas we found following results: 37 growth hormone (GH)-secreting adenomas, 23 prolactin (PRL)-secreting adenomas, 15 mixed GH-cell/PRL-cell adenomas, three mammosomatotroph cell adenomas, two adrenocorticotrophic hormone (ACTH)-secreting adenomas, one thyrotrophic cell adenoma, 18 gonadotroph adenomas, 30 null cell adenomas and 13 plurihormonal adenomas. No correlation was found between conventional features and the immunohistochemical profile. The immunohistochemical profile of functional pituitary adenomas is mandatory for a correct diagnosis. We revealed that staining characteristics of the tumor cells, such as acidophilic, basophilic or chromophobe are nowadays outdated as main principle of classification, because they not identify specific adenoma types.