A 9 year old male mixed-breed dog was presented for progressive aggressiveness towards the owner. The neurological evaluation was consistent with a forebrain syndrome. Magnetic Resonance Imaging (MRI) of the brain revealed enlargement of the third ventricle and presence of a large spheroidal neoplasm in the sellar/parasellar region suggestive of a pituitary macroadenoma. On the owner request, the dog was euthanized. Histopathological examination revealed the presence of a pituitary chromophobe carcinoma. To the author's knowledge, pituitary carcinomas have been rarely described in dogs, especially the chromophobe subtype.