Trans-sphenoidal surgery has a very low rate of complications despite a series of apparently negative anatomo-topographical factors. Complications may be either mechanical or functional, transitory or permanent. The most important complications are: hematoma of the focus, sub-arachnoid hemorrhage, empty sella, liquoral fistula, opto-chiasmatic lesions, arterial lesions, lesions of the cavernous sinus, parenchymal damage, nasal and paranasal mechanical lesions, insipid diabetes, hypopituitarism. The overall mortality rate is 0.4-1% and is always associated with predisposing factors, such as previous treatment, voluminous extrasellar growth, concomitant causes of disease; the most frequent causes of death are: hemorrhagic phenomena in the extrasellar portion of large size adenomas; vascular lesions involving the intracavernous carotid artery; and hypothalamic lesions. The frequency of major complications is in the region of 2.3%. Predisposing factors are: volume, consistency, invasiveness, previous treatment, intratumoral necrotic-hemorrhagic phenomena, age. Surgery is only indicated for some of the above complications, including hematoma of the focus, acute postoperative empty sella, rhinoliquorrhea resistent to conservative treatment, excessive filling of the sellar cavity. All the other possible complications are results or functional alterations which must be treated medically, even if a specific therapy only exists for some (such as early hypotonic polyuria). The series of patients reported here refers to the period 1978-1989 and accounts for a total of 259 trans-sphenoidal operations performed in 245 patients. Of the secondary operations, 6 were due to postoperative complications (hematoma of the focus in 2 cases, rhinoliquorrhea in 2 cases; empty sella and hemorrhagic infarction of a large suprasellar site in the 2 remaining cases). There were 2 deaths related to direct mechanical complications (both caused by hemorrhagic infarction of large tumoural residues and the surrounding cerebral parenchyma). Complications which did not require re-operating were observed in 11 further cases: 6 cases of persistent rhinoliquorrhea which required protracted spinal drainage; 2 cases of deterioration of previous visual deficits unrelated to either hematoma of the focus or empty sella but caused by trauma to optic structures, either directly or on a vascular basis; 3 cases of dyplopia due to oculomotory deficiency. In terms of hypophyseal function, the ex-novo onset of postoperative pan-hypopituitarism and insipid diabetes was only observed in one case.(ABSTRACT TRUNCATED AT 400 WORDS)