Background: The mechanism of hormonal effect on hematopoiesis is still obscure and only a few cases with bone marrow hypoplasia and pancytopenia which were related with hormonal insufficiency were reported. We had experience a case of pancytopenia and hyponatremia which were developed after the surgical removal of pituitary macroadenoma and radiotherapy on remnant mass. Case report: A 28-year-old man presented with pancytopenia and serum electrolyte abnormalities. He was diagnosed with acromegaly and had trans-sphenoidal approach for pituitary macroadenoma removal surgery at his age 22. After the surgery, there was some remnant adenoma and he had gamma-knife radiosurgery. Because of high serum GH level, he was on sandostatin suppression therapy. On following up, sandostatin was tapered out. Recent brain MRI showed empty sella and basal hormonal profile with combined pituitary stimulation test results showed pituitary hormonal deficiency except thyroid stimulating hormone(Table 1). In addition, his bone marrow biopsy finding showed hypocellular marrow. Fortunately with hypertonic saline, hyponatremia was corrected but pancytopenia was continued. Hormonal replacement was started with hydrocortisone. After a few days, leukocytes and platelet counts increased to near normal level. This has been sustained over 5 months follow up. Conclusion: Hypopituitarism is a possible cause of pancytopenia. Physicians need to consider hormonal insufficiency as a cause of pancytopenia developed in patients with previous history of surgery or radiation on pituitary gland.