OBJECTIVE To investigate the effect of spinal anesthesia on cerebral rSO2 during elective cesarean delivery (CD). METHODS Thirty-four women scheduled for elective CD under spinal anesthesia were recruited. In the operating room rSO2 of the left and right frontal area and right thigh was recorded using three disposable sensors. A combination of 1.8-2.0 ml of 0.75% ropivacaine plus 10 μg of fentanyl were injected intrathecally. Systolic and diastolic blood pressure, heart rate, SpO2 as well as rSO2 of the left and right forehead areas and right thigh were recorded before, 5, 10, and 25 to 50 minutes after spinal injection, after uterine incision and placenta delivery, and analyzed with ANOVA repeated measures. The study was approved by the Aretaieio Hospital Institutional Review Board and registered with ClinicalTrials.gov (ID: NCT01669135). RESULTS The rSO2 left and right frontal area values decreased significantly from baseline (p=0.0001 and p=0.0001 respectively), with most remarkable decreases 5 and 10 minutes after spinal injection, from 65 (SD 8.7)% to 56 (SD 9.3)% and 56 (SD 9.5)% (p=0.0001 and p=0.0001) for the left and from 63 (SD 7.7)% to 55 (SD 9.3)% and 56 (SD 8.9)% (p=0,0001 and p=0.0001) for the right frontal area respectively. The rSO2 right thigh values increased significantly during the study period (p=0.0001). CONCLUSIONS Contribution of extracranial circulation to the rSO2, lack of PaCO2 and cardiac output measurements. CONCLUSIONS Women undergoing CD under spinal anesthesia may present decreases in cerebral rSO2. The clinical impact of these results remains to be determined.