Obstructive sleep apnoea and type 2 diabetes are common medical disorders that have important clinical, epidemiological, and public health implications. Research done in the past two decades indicates that obstructive sleep apnoea, through the effects of intermittent hypoxaemia and sleep fragmentation, could contribute independently to the development of insulin resistance, glucose intolerance, and type 2 diabetes. Conversely, type 2 diabetes might increase predisposition to, or accelerate progression of, obstructive and central sleep apnoea, possibly through the development of peripheral neuropathy and abnormalities of ventilatory and upper airway neural control. Although more research is needed to clarify the mechanisms underlying the bidirectional association between the two disorders, their frequent coexistence should prompt all health-care professionals to embrace clinical practices that include screening of a patient presenting with one disorder for the other. Early identification of obstructive sleep apnoea in patients with metabolic dysfunction, including type 2 diabetes, and assessment for metabolic abnormalities in those with obstructive sleep apnoea could reduce cardiovascular disease risk and improve the quality of life of patients with these chronic diseases.