Objective To investigate whether somatostatin analog octreotide long acting release (LAR) shrinks growth hormone (GH) secreting adenomas, and improves the results of subsequent transsphenoidal surgery. Methods Seventeen previously untreated active acromegalic patients with pituitary adenomas were treated with LAR (30 mg intramuscular injection every 28 days) for 3 months prior to transsphenoidal surgery. Clinical reaction, mean GH secretion, and tumor volume were measured under basal conditions and after LAR treatment. Results Presurgical treatment improved acromegaly symptoms and induced a significant reduction of GH under the 5 ng/mL limit in microadenoma (P < 0.05), while only 18.2% (2/11) in macroadenoma. Meanwhile, tumor shrinkage occurred in 58.8% (10/17) patients, with 1 case in the microadenoma group. All marked shrinkage (> 25%) occurred in the macroadenoma group. Statistical analysis showed tumor shrinkage caused by LAR was greater in macroadenoma group than that in microadenoma group (P < 0.05). During operation, adenoma was soft in 15 cases, with the exception of 2 cases in which the soft tumor was divided by fibrous septa, but all tumor removal was smooth. Conclusions A short term administration of preoperative LAR may induce a significant decrease in GH-secretion level and adenoma volume. Presurgical use of octreotide LAR improves surgical results especially in macroadenomas. Methods Seventeen previously untreated active acromegalic patients with pituitary adenomas were treated with LAR (30 mg intramuscular injection (LAR) shrinks growth hormone (GH) secreting adenomas, and improves the results of subsequent transsphenoidal surgery. Results Forurgical treatment improved acromegaly symptoms and induced a significant reduction of GH under the 5 ng / All marked shrinkage (> 18%) in macroadenoma. While the number of tumor shrinkage occurred in 58.8% (10/17) patients, with 1 case in the microadenoma group. 25%) occurred in the macroadenoma group. Statistical analysis showed tumor shrinkage caused by LAR was greater in macroadenoma group than that in microaden During operation, adenoma was soft in 15 cases, with the exception of 2 cases in which the soft tumor was divided by fibrous septa, but all tumor removal was smooth. Conclusions A short term administration of preoperative LAR may induce a significant decrease in GH-secretion level and adenoma volume. Presurgical use of octreotide LAR improves surgical results especially in macroadenomas.