Hypertension is classified as idiopathic or secondary. In animals with idiopathic hypertension, persistently elevated blood pressure is not caused by an identifiable underlying or predisposing disease. Until recently, more than 95% of cases of hypertension in humans were diagnosed as idiopathic. New studies have shown, however, a much higher prevalence of secondary causes, such as primary hyperaldosteronism. In dogs and cats, secondary hypertension is the most prevalent form and is subclassified into renal and endocrine hypertension. This review focuses on the most common causes of endocrine hypertension in dogs and cats.