Pituitary macroadenomas are becoming more prevalent in veterinary medicine. This paper discusses a 10 year old female, spayed Beagle that presented to the Cornell Hospital for Animals with the chief complaints of mental dullness, pacing, staring at walls, polyuria, and polydyspia. The past history included a great appetite, increased drinking and urination habits and progressive lethargy. On physical examination the only abnormalities noted were a previously diagnosed heart murmur, left hind limb lameness due to previous cranial cruciate rupture and subsequent surgical repair, mental dullness, pot-belly appearance and pain on palpation of the head and neck. Initial diagnostics pursued were a complete blood count, chemistry panel, urinanalysis, endogenous ACTH test and low dose dexemethasone suppression test. The results of these initial diagnostics gave the presumptive diagnosis of pituitary dependent hyperadrenocorticism. Due to the neurological signs on presentation, and head and neck pain elicited, an MRI scan was also performed. This revealed a 14 x 17x 20 mm mass in the region of the pituitary gland. Final diagnosis was of a pituitary macroadenoma. Radiation therapy was employed to treat the pituitary macroadenoma. The treatment was successful with a reduction of the neurological signs. Medical management was used to control the signs of hyperadrenocorticism. Discussion of this case as related to pituitary dependent hyperadrenocorticism and specifically pituitary macroadenomas is outlined below.