Background In the present study, we aimed to determine the effect of different positive end-expiratory pressure (PEEP) levels on the cross-sectional area (CSA) of the right internal jugular vein (RIJV) and the overlap index between the RIJV and the right common carotid artery (RCCA) in mechanically ventilated patients with laryngeal mask airway (LMA) insertion. Material/Methods A total of 60 patients who were scheduled for elective surgery under general anesthesia with LMA insertion were enrolled. After LMA insertion, the image of RIJV and RCCA were taken after applying 4 different PEEPs in a random order: 0 (P0), 5 (P5), 10 (P10), and 15 (P15) cm H 2 O. The CSA, transverse and anteroposterior (AP) diameters of the RIJV, and the overlap index were measured. Results Compared to group P0, the overlap indexes of P10 ( P =0.0032) and P15 ( P <0.001) were significantly increased, but without a significant trend toward further increases in group P15. PEEP at 10 and 15 cm H 2 O increased CSA, transverse and AP diameter of the RIJV in comparison to group P0 (all P <0.001). There was a statistically significant increase in CSA of the RIJV in P15 compared with P10 by 12.2% ( P <0.001), but did not reach the relevant cut-off value (ΔCSA ≥15%). Conclusions The application of PEEP at 10 cm and 15 cm H 2 O in patients receiving mechanical ventilation with LMA insertion significantly increases the size of the RIJV. However, the overlap index between the RIJV and the RCCA increased as well.