Abnormalities in carbohydrate metabolism appear to be the most prevalent metabolic disorder among those associated with fluctuating and/or progressive sensorineural hearing loss, tinnitus and vertigo; investigating these abnormalities is therefore an essential part of the diagnostic and therapeutic management of these patients. Carbohydrate metabolic disorders encompass a wide range of metabolic manifestations, each with its own specific features in terms of presentation, diagnosis and management; however, viewed as a whole, they likely represent different stages of the same pathophysiological process. The most important metabolic manifestations are discussed below.