Objective : Microscopic and endoscopic transsphenoidal approach (TSA) are major surgical techniques in the treatment of pituitary adenoma. Endoscopic endonasal transsphenoidal approach (EETSA) has been increasingly used for pituitary adenomas, however, its surgical outcome particularly in functioning pituitary adenoma has been debated. Here, we investigated the endocrine outcome of the patients with growth hormone (GH) and adrenocorticotropic hormone (ACTH) secreting pituitary adenoma treated by EETSA. Methods : We treated 80 patients with pituitary adenoma by EETSA since 2004, of which 12 patients were affected by functioning pituitary adenomas (9 GH, 3 ACTH, 0 PRL; 9 macro, 3 micro). Surgical outcome of those patients treated by EETSA was compared with that of the 11 functioning pituitary adenoma patients (8 GH, 3 ACTH; 8 macro, 3 micro) who underwent sublabial microscopic TSA between 1997 and 2003. Results : Imaging remission based on postoperative MRI was achieved in 8 (73%) and hormonal remission in 5 (45%) of 11 patients treated by sublabial microscopic TSA. Imaging remission was observed in 10 (83%, p=0.640) and hormonal remission in 10 (83%, p=0.081) of 12 patients by EETSA. CSF leakage was noticed in 2 (17%) of EETSA group and in 2 (18%) of sublabial microscopic TSA group. Panhypopituitarism was observed in 1 (9%) of EETSA group and in 3 (27%) of sublabial microscopic TSA group. Conclusion : EETSA appears to be an effective and safe method for the treatment of functioning pituitary adenomas.