We have encountered a case of a pituitary mass which emerged and enlarged during pregnancy in a 29-year-old woman. On CT scaning the mass disappeared over the course of four months postpartum and was followed by pituitary hypofunction. The hypofunction was restricted to ACTH, GH, and PRL. The visual field defects, bitemporal hemianopsia, disappeared with disappearance of the pituitary mass on CT scanning, indicating that such deficits during this period were reversible. Based on the clinical course and laboratory data, this case is thought to have been lymphocytic adenohypophysitis. It was concluded that among pituitary tumors developing during pregnancy there are some such cases which do not require surgical therapy.