We applied near-infrared spectroscopy (NIRS) to assess cerebral tissue oxygenation and hemodynamics in obstructive sleep apnea (OSA) sufferers and control volunteers. We designed NIRS sensors and applied measurement schemes that included certain polysomnography parameters, such as arterial hemoglobin oxygen saturation (SaO2), heart rate (HR), and respiratory signal (RS), together with NIRS parameters, such as oxy- ([O2Hb]), deoxy- ([HHb]), total hemoglobin ([tHb]) concentrations, and tissue hemoglobin oxygen saturation (SO2). Twenty-one volunteers (8 females, 13 males, age 22-74 years) participated in the study. Eight were OSA sufferers, while 13 constituted the control group. Measurements were conducted during breath holding exercises and 30-45 minute daytime naps. In comparing OSA subjects with controls during breath holding, a smaller increase or even a decrease in SO2, [O2Hb], and [tHb] and a simultaneous larger increase in [HHb], confirmed insufficiency of the circulatory compensatory mechanism that prevents brain tissue hypoxia. Changes in cerebral oxygenation and hemodynamics due to hypoxia during breath holding showed statistically significant differences (p<0.05) between control and OSA subjects and between non-snorers and OSA subjects (p<0.03 for Δ[O2Hb], Δ[HHb], Δ[tHb], and ΔSO2). NIRS provides the clinician with important, direct insight on the cerebral tissue oxygenation and hemodynamics related to the chronic intermittent hypoxia in OSA for potential identification of individuals at risk for cerebrovascular morbidity. © 2003 WebSciences.