The aim of the work is to analyze preoperative predictors and their effect on results and outcomes following endoscopic endonasal transsphenoidal surgery (EETSS) for functioning pituitary adenomas, for this purpose; 99 patients were studied. All these patients were subjected to:  Full data collection (personal history, history of present illness, past history)  Clinical examination included general, neurological, and endocrinological examinations.  Complete general examination including; vital signs (pulse, blood pressure, temperature), head, neck, chest, and abdominal examination.  Neurological examination at admission included: cranial nerve palsy (3rd, 4th, and 6th), altered level of consciousness, visual impairments (decreased visual acuity, visual field defects).  Visual Examination (within 24 to 48 hours after admission): all patients proceeded to have formal visual field charting by an ophthalmologist.  Laboratory investigations: routine laboratory work & hormonal assays preoperative (basal) and postoperative as serum prolactin (PRL), growth hormone (GH), insulin-like growth factor (IGF-1), thyroid stimulating hormone (TSH), adrenocorticotropic hormone (ACTH), luteinizing hormone (LH), follicle stimulating hormone (FSH), free thyroxine (FT4), free triiodothyronine (FT3), serum cortisol and urinary free cortisol.  Neuroimaging studies: computerized tomography (CT) with and without contrast was performed on both brain and paranasal sinuses and MRI brain without & with contrast was performed  Management: In patients with prolactinoma, treatment started with medical therapy in the form of dopamine agonist e.g. Parlodel or Summary 131 dostinex and the endoscopic endonasal trans-sphenoidal surgical approach was used for tumor removal in all patients.  Histopathological examination, including immunohistochemical staining, was conducted.  Follow up protocol: all patients underwent CT brain immediately postoperatively and an MRI three months later to evaluate the extent of resection; this was then repeated annually.  Post-surgical ophthalmological examination and assessment of endocrine function were performed 3 months post-surgery, and then every 6 months thereafter. Our study reveals the following:  Males are affected more than females with mean age 42.5 years.  Irregular menstruation was the most common presenting symptoms among the study population in 22 patients (22.2%), followed visual disturbance in 17 patients (17.2%), acromegaly and increased intracranial pressure (inform of combination of headache, nausea, vomiting & visual disturbance) were in third place with each one 14 patients (14.1%), then headache with 11 patients (11.1%), 8 cases (8.1%) were accidentally discovered, 5 cases (5.1%) had Cushing disease, also 5 cases (5.1%) had sexual dysfunction, finally 3 cases (3%) were recurrent pituitary adenomas.  41 cases (41.4 %) were macrooadenoma (> 1cm), while 38 cases (38.8 %) were microadenoma (4cm).  55 patients (55.6%) were prolactiomas, while 17 patients (17.2%) were GH - secreting adenomas, 11 patients (11.1%) were Gonadotropin hormone - secreting adenomas, 6 patients (6.1%) were ACTH - secreting adenomas, 2 patients (2%) were thyrotropin (TSH) -secreting adenomas and 8 patients (8.1%) were multiple hormones secreting adenomas. Summary 132  79 patients (79.8%) underwent gross total resection of the tumor, while 20 patients (20.2%) underwent subtotal resection of the tumor.  The mean KI 67 labeling index was 2.5±2.2 %  The mean follow up duration was 12.9±7.6 months.  93 patients (93.9%) were clinically improved while 6 patients (6.1%) were not improved. Also, we found that 60 patients (60.6%) were improved hormonally while 39 patients (39.4%) were not improved.  64 patients (64.6%) passed without complications but 35 patients (35.4%) had complication inform of 14 patients (14.1%) had hypopituitarism, 5 patients (5.1%) had transient diabetes insipidus, 5 patients (5.1%) had csf leak, 4 patients (4%) had hyponatremia, 4 patients (4%) developed anosmia, 2 patients (2%) had epistaxis and one patient (1%) died due to acute hydrocehallus and cerebral haemorrhage.  After neuroimaging (MRI) follow up; 79 patients (79.8%) were totally removed and 20 patients (20.2%) had residual of the tumor.  There was no significant relation between age of the studied patients and hormonal improvement, post-operative complication & MRI follow up.  There was highly statistically significant relation between tumor sizes, hormonal improvement and MRI follow up but no significant relation between tumor size and postoperative complications. As 94.7% of patients with microadenoma showed hormonal improvement (p=0.000) and 73.7% of patients with microadenoma showed no residual mass on MRI follow up (p =0.000).  No significant relation between hormonal typing of the studied patients and hormonal improvement, post-operative complication & MRI follow up.  There was highly statistically significant relation between extent of resection of the tumor, hormonal improvement & MRI follow up and statistically significant relation between extent of resection of the tumor & postoperative complications. As 62% of patients with totally resected tumors showed hormonal improvement (p=0.000), 100% of patients Summary 133 with totally resected tumors showed no residual mass on MRI follow up (p =0.000) and 69.6% of totally resected tumors didn't have postoperative complication (p=0.04).  There was no significant relation between Ki-67 Labeling Index of the studied patients and hormonal improvement, post-operative complication & MRI follow up