Aim. To evaluate the impact of hyperglycemia concurrent with obstructive sleep apnea syndrome (OSAS) on endothelial function (EF) and vessel remodeling in patients with Grade 1—2 hypertension. Subjects and methods. A total of 101 patients with Grade 1—2 hypertension were examined. A study group (SG) consisted of 74 hypertensive patients with type 2 diabetes mellitus (T2DM). A control group (CG) comprised 27 persons with isolated blood pressure (BP) elevation. The patients with T2DM underwent cardiorespiratory sleep monitoring, the readings of which were used to divide SG into 2 subgroups: 1) patients with an apnea-hypopnea index of <30 episodes/h (SG-1); 2) those with an index of >30 episodes/h (SG-2). 24-hour BP and vascular stiffness monitoring was made; EF was evaluated; common carotid artery diameter (CCAD) and intima-media thickness (IMT) were determined. Results. The diabetic patients showed lower central diastolic BP and higher aortic pulse BP. Unlike the comparison group, the diabetic patients with severe OSAS were found to have the highest central pulse wave propagation velocity at night. There was a preponderance of an average nocturnal arterial rigidity index, average daily and average nocturnal BP rising rates, and shorter reflected wave propagation time in the diabetic patients. The mean level of flow-mediated vasodilation was significantly reduced in SG-2. The diabetic patients, unlike the controls, were ascertained to have decreased absolute responsiveness index values. There were increases in IMT and CCAD in SG-2. Conclusion. OSAS worsens EF and vessel rigidity in patients with T2DM concurrent with hypertension.