A feline, male, 12 years of age, mixed breed was attended at the Veterinary Hospital of the State University of Londrina, showing apathy, paresis, cervical ventroflexion, sialorrhea, mydriasis and blindness. Complementary exams showed azotemia, hypokalemia and a unilateral adrenal nodule. The measurement of serum aldosterone confirmed the diagnosis of hyperaldosteronism caused by adrenal adenoma. After three months of oral medication, a surgical excision of the adrenal gland was performed and, 72 hours later, the patient died of renal complications. This study highlights the importance of considering primary hyperaldosteronism as a relevant differential in cats with hypokalemia and hypertension.