Epidemiologic evidences suggest that obstructive sleep apnea syndrome(OSAS) itself induces risk factors for cardiovascular diseases(= insulin resistance) independent of obesity. Our data suggest that moderate to severe OSA(AHI = > 20) is a contributing factor to the development of hyperinsulinemia, abnormal glucose metabolism and non-insulin-dependent diabetes mellitus(NIDDM) independent of aging, obesity and hereditary predisposition for DM in patients with OSAS. On the other hand, disagreement exists as to the incidence of OSAS in DM patients. Some authors reported that the incidence of OSAS was high among patients with DM, while others did not find such relationship. In these studies, the number of cases studied was small and, in addition, the selection of patients may have been biased. Future clinical research is needed to answer this issue.