Several studies have shown a correlation between obstructive sleep apnea (OSA) and obesity, as well as obesity and diabetes mellitus. This is probably related to the fact that patients with OSA are likely to have a high prevalence of the risk factors that comprise metabolic syndrome. It has been shown that sleep deprivation when induced experimentally can cause glucose intolerance and many studies have established the association between sleep apnea and type two diabetes mellitus. There is also a proven association between snoring and sleep apnea as well as snoring and metabolic syndrome. In the current article we review the patho-physiology of hyperglycemia, insulin resistance due to sleep apnea, and treatment of OSA with continuous positive airway pressure therapy. Continuous positive airway pressure (CPAP) does, in fact, lead to improvement in insulin resistance and lowered hemoglobin A1C levels. The question that remains to be answered is whether the association between sleep apnea and the components of metabolic syndrome is one of co-existence or causality, but it can no longer be denied that there is a strong relationship which should lead to investigation of one if the other is found.