Background and Purpose-We measured arterial oxygen saturation (SaO(2)) during eating in acute stroke patients to establish the frequency of any meal-related hypoxemia, which could further damage already vulnerable brain tissue. Methods-Stroke patients (less than or equal to 12 days from stroke onset) classified as “safe to feed orally” were compared with elderly hospitalized (for nonneurological causes) and young healthy controls. SaO(2) was measured noninvasively at the bedside by pulse oximetry continuously for 10 minutes before the patient ate a meal, during the meal, and for 10 minutes after completion of the meal. Results-The median baseline SaO(2) was significantly lower in stroke patients (n=106, 95.7%) than elderly (n=50, 96.7%) or young control subjects (n=20, 97.9%; P<0.001), There was a small decrease in the median SaO(2) during eating in stroke and elderly patients (95.6%, P=0.08, and 96.3%, P=0.004, respectively) but not in young controls. Only stroke patients had a significantly lower median Sao, after completion of the meal (95.4%, P<0.001). SaO(2) of less than or equal to 90% during and after eating occurred in 24% of stroke and 16% of elderly patients but not in young controls, and it was significantly more common in those who had SaO(2) of less than or equal to 90% during the baseline recordings (P less than or equal to 0.003). Conclusions-Eating a meal was associated with a small fall in median Sao, among stroke and elderly patients, but only in stroke patients did this persist for at least 10 minutes after eating. A quarter of stroke patients had episodes in which the Sao, fell to less than or equal to 90% saturation (ie, hypoxemia) during or after eating, although this rarely coincided exactly with swallowing and was more common in patients who also experienced desaturation during the baseline recordings. Further studies are required to establish whether these changes are clinically important.