The preoperative diagnosis of pituitary abscess is difficult. The case of a 56-year-old man with a pituitary abscess and painless thyroiditis is presented. There has been no previous such report. The differential diagnosis includes pituitary abscess, lymphocytic adenohypophysitis or infundibuloneurohypophysitis, share clinical symptoms of panhypopituitarism and diabetes insipidus, and is of critical importance as the treatment of these conditions differ. The association with painless thyroiditis suggests a diagnosis of lymphocytic adenohypophysitis or infundibuloneurohypophysitis. However, the coincidence of pituitary abscess and painless thyroiditis was observed in our patient, and thus though rare, should be considered. Surgical exploration and histopathological examination are essential for the differential diagnosis of these diseases.