Background: Cerebrospinal Fluid (CSF) leak during endonasal endoscopic pituitary adenoma surgery is an important factor that affects the way of sellar floor closure, postoperative CSF leak rate and postoperative outcome. This study aimed to improve the outcome of patients with intraoperative cerebrospinal fluid leak during endoscopic pituitary surgery. Methods: on 18 patients diagnosed with pituitary adenoma. These patients underwent resection through endonasal transsphenoidal approach with the use of intrathecal fluorescein injection. Results: With the use of intrathecal fluorescein, intraoperative CSF leak appeared to be higher than usual. Intraoperative CSF leak occurred in 15 patients (83.3%). As regard grades of CSF leak, 11 patients had grade 1(61.1%), 3 patients had grade 2(16.7%) and only one patient had grade 3 (5.6 %). Fluorescein injection was done for patients with no CSF leak or suspicion of CSF leak but not done for grade 2 and 3, hence, it was done for 14 patients (77.8%) and in 7 of them (50%), CSF leak appeared only with Fluorescein, in 4 of them (28.5%) suspicious leak was confirmed with Fluorescein and 3 of them (21.5%) had no CSF leak confirmed with no Fluorescein appearance after injection. Postoperative CSF leak occurred in 3 of 18 patients (16.7%) and relieved in all patients after few days with lumbar drain kept in place till CSF leak stopped. Conclusion: The use of intrathecal fluorescein during endoscopic transsphenoidal pituitary surgery is very helpful in identifying intraoperative CSF leak especially G1 leak, resulting in better sellar closure and less postoperative CSF leak.