Objective: We investigated glucose metabolism and insulin resistance in non-obese and moderately overweight sleep apnea patients, as well as their response to nasal CPAP treatment.Methods: A group of subjects with glucose intolerance was screened for sleep disordered breathing by clinical interview and ambulatory recordings. Ten subjects were found to have untreated sleep apnea and were asked to participate in further investigation. This included nocturnal polysomnography, oral glucose tolerance test and indirect calorimetry. Subjects then had calibration of nasal CPAP with polysomnography. Two months after start of treatment, all subjects were restudied as at baseline. In parallel, six obstructive sleep apnea syndrome (OSAS) subjects, diagnosed through the sleep clinic, were matched for gender, age and oxygen desaturation index with the other group, and had a euglycemic hyperinsulinemic clamp at baseline and after 2 months of nasal CPAP.Results: The first ten patients showed no change in total glucose oxidation, glucose oxidation by weight or by fat free mass, or insulin energetic expenditure, despite nocturnal usage of nasal CPAP. Similarly, when comparing baseline to the treatment at 2 months, the six OSAS patients had no change in mean glycemia, insulin, C peptide and hemoglobin (Hgb) A1C measurements. No difference in the amount of glucose infused during the duration of the clamp was noted either.Conclusion: Our data do not support the existence of a significant relationship between glucose and insulin metabolism and obstructive sleep apnea. Obesity, when present, is the important variable.