A 15-year-old, spayed female maltese dog was presented with polydipsia, polyuria, polyphagia, abdominal distention, alopecia and hyperpigmentation. The complete blood counts were in normal range, and the serum biochemistry revealed elevated level of glucose and globulin. Mild hepatomegaly was seen on radiography of abdomen. Abdominal ultrasonography revealed the uniformly enlarged left adrenal gland measured 2.4 cm in diameter. ACTH stimulation test and LDDST revealed hyperadrenocorticism. HDDST revealed pituitary dependent hyperadrenocorticism. On CT images, isodense mass with contrast enhancing was seen in left adrenal gland. Cytologic result is consistent with benign tumor. Adrenal mass was surgically removed and evaluated. Histopathologic examination revealed adenocortical adenoma.