Increased circulating endothelial cells (CECs) have been observed in patients with vascular injury associated with acute myocardial infarction, pulmonary hypertension, and congestive heart failure. Decreased circulating endothelial progenitor cells (EPCs) have been observed in patients with risk factors for cardiovascular disease. Obstructive sleep apnea (OSA) is associated with increased risk of cardiovascular disease and endothelial dysfunction. Subjects were recruited from patients referred for overnight polysomnograms; 17 subjects had OSA and 10 control subjects did not have OSA. All subjects lacked vascular disease and risk factors for vascular disease. Peripheral blood was obtained from fasting subjects in the morning, following sleep studies. CECs and EPCs were quantified using magnetic bead separation with UV epifluorescence microscopy and flow cytometry immunophenotyping, respectively. Cell counts and demographic variables were compared using unpaired t tests. Regression analysis was performed comparing cell counts with the apnea-hypopnea index (AHI) and nadir SaO2. Subjects with OSA and controls did not differ significantly in terms of age and body mass index. Subjects with OSA had higher AHI, lower nadir SaO2, and greater sleepiness (Epworth Sleepiness Scale scores). There were no significant differences in CEC (7.0 ± 1.5 vs. 4.9 ± 0.9, p > 0.05) or EPC (1077 ± 318 vs. 853 ± 176, p > 0.05) between controls and OSA cases, respectively. In this small study, we found no differences in CECs or circulating EPCs between patients with OSA and controls. OSA may not be associated with these markers of vascular endothelial cell injury in patients with no concomitant vascular disease.