Primary hyperaldosteronism (PHA) is being recognized more frequently in cats. Usual hallmarks of the disease include hypokalemia and systemic hypertension. Ultrasound frequently detects an abnormality in the affected adrenal gland. Diagnosis is based on increased plasma or serum aldosterone concentrations, particularly in the face of hypokalemia and low renin activity (when measurement is available). Cats with PHA have good prognoses with surgical excision of tumor-bearing adrenal glands. Medical management can stabilize patients for many months. The reported incidence is likely to increase as practitioners become more aware of the condition and diagnose it earlier in the disease course. If veterinarians choose to use humans as an experimental model, PHA should be considered a differential for cats with hypertension of unknown cause or that is refractory to treatment. Using hypokalemia as a definitive criterion in screening for PHA may result in late-stage diagnosis and underrecognition of incidence of PHA in the hypertensive population.