Abstract During the past decades obesity and diabetes have become increasingly common in modern, industrialized societies. At the same time sleep disorders, chronic sleep loss and sleep deprivation have also become more and more prevalent. There may be a positive feed back circle between the two disorders: sleep problems may affect endocrine function and metabolic conditions, while metabolic abnormalities potentially interfere with sleep regulation. Sleep-disordered breathing, obstructive sleep apnea in particular, has the strongest association with glucose metabolism. Prevalence and severity of obstructive sleep apnea are higher among diabetic individuals compared to non-diabetic subjects. Central obesity is an important risk factor both in diabetes and sleep apnea, and recent evidence supports the direct association between them. Diabetic neuropathy and metabolic syndrome parameters correlate with the presence and severity of obstructive sleep apnea. Intermittent hypoxia may cause insulin resistance, consequently increasing the risk of diabetes and further impairing glycemic control. Specialists in both diabetology and sleep medicine need to work together to prevent the negative interactions between these two groups of disorders and to also preserve patients' quality of life and to improve outcomes.