In two patients with lymphocytic adenohypophysitis, images of the pituitary gland were serially observed by MRI. In both cases, the pituitary gland had swollen during the late stage of the first pregnancy. In case 1, MRI findings were representative of lymphocytic adenohypophysitis. After delivery, plasma levels of PRL, ACTH and cortisol decreased markedly. The height of the pituitary gland gradually decreased from 22 mm (14 days after delivery) to 13 mm (73 days) and became rapidly smaller (4.9 mm, 115 days) following administration of massive doses of hydrocortisone for the treatment of acute adrenal insufficiency induced by painless thyroiditis. Six years later, the height was 2.5 mm. Low plasma levels of PRL and cortisol persisted. Diabetes insipidus did not develop. In case 2, MRI revealed a pituitary mass accompanied by a cystic change. Lymphocytic adenohypophysitis was confirmed by histological examination. Because pituitary function tests indicated that ACTH, PRL, GH and TSH were of low levels, hydrocortisone and L-thyroxine were orally administered. No diabetes insipidus was demonstrated. MRI disclosed that the height of the pituitary gland was 23 mm (17 days after delivery) but decreased to 17 and 5.5 mm after 44 and 128 days, respectively. Four years later immediately after the second delivery, it was 1 mm, and the patient was diagnosed as having empty sella. Long-term observation of lymphocytic adenohypophysitis demonstrated that the pituitary gland was markedly atrophied, leading to empty sella. It is believed that some of the classic cases of Sheehan's syndrome associated with empty sella may include lymphocytic adenohypophysitis.