To describe clinical and subclinical characteristics of sleep apnea syndrome (SAS) in patients with type 2 diabetes mellitus (T2DM). Subject and methods: A descriptive cross-sectional study in 69 patients with type 2 diabetes mellitus measured as polysomnograms or ventilatory polygraphy at Bach Mai Hospital. Results: Sleep apnea syndrome was present in 85,5% of patients with type 2 diabetes mellitus. BMI was higher in the diabetic group with sleep apnea syndrome than in the group without sleep apnea. The STOP-BANG and Epworth screening scores were higher in the patients with sleep apnea syndrome group with p<0,05. There was no difference in HbA1c and fasting glucose between the two groups of patients. In the group of patients with type 2 diabetes mellitus with SAS, the mean apnoea/hypopnoea index (AHI) was 33,8±25 and the oxygen desaturation index (ODI) was 39 ± 31,2, which were higher than those without sleep apnea syndrome with p<0,05. Besides, the statistically significant difference (p < 0,05) in the lowest SpO2 index in the two patients studied was also higher in the group with sleep apnea syndrome. The lowest SpO2 value in the group of type 2 diabetes with sleep apnea was statistically significantly lower than the group without sleep apnea. Conclusions: Sleep apnea syndrome is common in patients with type 2 diabetes. STOP-BANG and Epworth are effective tools to screen for sleep apnea syndrome among patients with type 2 diabetes.