The aim is to present unusual clinical course and magnetic resonance imaging (MRI) features of pituitary abscess. A 59-year-old man presented with fever, polyuria, polydipsia and marked weight loss within the last two months. Basic endocrinology tests revealed the presence of anterior pituitary dysfunction, associated with central diabetes insipidus and increased levels of inflammatory markers. The presence of expansile sellar lesion, showing restricted diffusion signal pattern compatible with acute pituitary pyogenic abscess was found on MRI. Regression of pituitary abscess was obvious during the next few weeks of parenteral antibiotic treatment. Adequate substitution treatment with L thyroxine, hydrocortisone, testosterone and desmopressin was achieved. Seventeen months later, clinical deterioration associated with recurrent pituitary abscess was confirmed on MRI. Abscess regression was obvious again after conservative treatment. However, control MRI study performed three years after initial scanning revealed the presence of pituitary tumor, most consistent with macroadenoma. Surgical intervention was ordered. Histologic evaluation indicated the presence of fibrotic changes, associated with granulation tissue and rare cellular elements, compatible with chronic inflammation. To the best of our knowledge, there are no studies in the literature describing such a pattern of chronic evolution of pyogenic pituitary abscess with consequent chronic inflammatory changes with granulation tissue proliferation, mimicking macroadenoma.