The pituitary stalk (PS) is a relatively thin bundle connecting the hypophyseal stalk to the pituitary gland; it consists of both axons of the hypothalamic nuclei (terminating in the neurohypophysis) and the system of portal vessels. Compression of the PS by a space-occupying lesion or its transection (forced or intended) during surgery may lead to the development of endocrine disorders: hypopituitarism, diabetes insipidus, and hyperprolactinemia. The modern literature lacks studies evaluating the severity of endocrine disorders depending on the PS condition before and after surgery. Purpose. The study purpose was to investigate endocrine disorders in patients with sellar region (SR) tumors and the PS that was compressed before surgery and preserved or transected during a neurosurgical intervention. Material and methods. The study included 139 patients with various SR tumors. In 82 patients, a preoperatively compressed PS was preserved (41 patients with hormonal inactive adenoma (HIA) and 41 patients with suprasellar meningioma); in 57 patients, the PS was transected during surgery (46 patients with pituitary stalk craniopharyngioma and 11 patients with hormonally inactive endosuprasellar pituitary adenoma). The hormonal status (PRL, TSH, LH, FSH, fT4, cortisol, testosterone, or estradiol) was examined in all patients both before and after surgery. Results. Hyperprolactinemia was preoperatively detected in 37% of patients with tumors compressing the PS. Elimination of PS compression (tumor resection) led to normalization of the PRL level in most patients and was not accompanied by aggravation of hypopituitarism symptoms. Transection of the PS caused panhypopituitarism in 100% of patients and diabetes insipidus in 93% of cases. After transection of the PS, hyperprolactinemia did not develop in 59% of patients with craniopharyngiomas (CPs) and 82% of patients with HIA. Conclusions. Given the difference in symptoms associated with compression and surgical transection of the PS, we believe that these two concepts should be clearly distinguished. The PS compression syndrome includes primarily hyperprolactinemia (37% of cases); elimination of PS compression leads to normalization of the PRL level in most patients and is not accompanied by aggravation of hypopituitarism symptoms. The PS transection syndrome in patients with CP and HIA led to the development of panhypopituitarism in all patients and permanent diabetes insipidus in most of them. The causes of the absence of hyperprolactinemia in many patients with PS transection require further research. The surgeon planning intraoperative PS transection to increase the radicality of surgery should be well informed about the consequences of this procedure for the patient’s endocrine status.