A 6-year-old spayed female cat was evaluated for uncontrolled diabetes mellitus and poor hair coat. Clinicopathologic abnormalities included high serum activity of liver enzymes, hyperglycemia, hypercholesterolemia, glucosuria, and an exaggerated response to ACTH stimulation. Abdominal ultrasonography revealed large adrenal glands. Hyperadrenocorticism was diagnosed. Treatment for a facial abscess was instituted along with administration of metyrapone for hyperadrenocorticism. After stabilization, bilateral adrenalectomy was performed. The cat recovered without complications and has remained clinically normal for 5 months with treatment of desoxycorticosterone pivalate and prednisone. Treatment with metyrapone appeared to stabilize the cat metabolically and clinically prior to surgery.