Phaeochromocytomas are rare adrenal tumours characterized by the overproduction of catecholamines. They are often misdiagnosed due to their non-specific clinical signs. This chapter focuses primarily on the canine disease as phaeochromocytoma is extremely rare in cats. The chapter explains the process of catecholamine synthesis and metabolism within the adrenal gland, as well as the clinical signs and diagnostic imaging techniques used to detect phaeochromocytoma. Treatment options are addressed, including adrenalectomy and medical management with tyrosine kinase inhibitors.