Diabetic autonomic neuropathies are a heterogeneous and progressive disease entity and commonly complicate both type 1 and type 2 diabetes mellitus. Although the aetiology is not entirely understood, hyperglycaemia, insulin deficiency, metabolic derangements and potentially autoimmune mechanisms are thought to play an important role. A subgroup of diabetic autonomic neuropathy, cardiovascular autonomic neuropathy (CAN), is one of the most common diabetes-associated complications and is ultimately clinically important because of its correlation with increased mortality. The natural history of CAN is unclear, but is thought to progress from a subclinical stage characterized by impaired baroreflex sensitivity and abnormalities of spectral analysis of heart rate variability to a clinically apparent stage with diverse and disabling symptoms. Early diagnosis of CAN, using spectral analysis of heart rate variability or scintigraphic imaging techniques, might enable identification of patients at highest risk for the development of clinical CAN and, thereby, enable the targeting of intensive therapeutic approaches. This Review discusses methods for diagnosis, epidemiology, natural history and potential causes and consequences of CAN.