Hyperadrenocorticism, a disorder characterized by excessive production of cortisol by the adrenal cortex, is well-recognized in dogs. A 10-year-old, intact male, Yorkshire terrier dog was evaluated because of corneal ulceration and generalized alopecia. Diagnosis was made based on history taking, clinical signs, physical examination, and results of routine laboratory testing (complete blood count, serum biochemical analysis, and urinalysis). In addition, adrenocorticotropic hormone (ACTH) stimulation test and abdominal ultrasonography were also used to diagnose this case. The patient was diagnosed as adrenal gland neoplasia and medical therapy using the adrenocorticolytic agent, mitotane, was initiated. An ACTH stimulation test was performed after initial therapy. After successful induction was obtained, maintenance therapy with mitotane still continued.