Sleep is an essential part of our daily living, and sleep disturbances may intervene with the biological and physiological processes in human body leading to the development of metabolic dysfunction. Short sleep duration and poor sleep quality have adverse effects on metabolism and hormonal processes, contributing to increased cardiovascular risk. Obstructive sleep apnoea is a chronic condition characterized by repetitive upper airway collapse during sleep, causing intermittent hypoxaemia, recurrent arousals and sleep fragmentation. Sleep disturbances can increase sympathetic activity, provoke systemic inflammation and oxidative stress, and impair vascular endothelial function. Obstructive sleep apnoea is increasingly recognized to be an independent cardiovascular risk factor. There is intense research interest in the association between obstructive sleep apnoea and the metabolic syndrome - the constellation of inter-related metabolic derangements including central obesity, hypertension, insulin resistance and dyslipidaemia, which appears to directly promote the development of atherosclerosis. The underlying pathophysiologic pathways or mechanistic links between obstructive sleep apnoea and metabolic syndrome have not been well delineated. This article reviews the current knowledge of the relationship between sleep disturbances, sleep-disordered breathing and the metabolic syndrome in adults.