BACKGROUND Resuscitative endovascular balloon occlusion of the aorta (REBOA) is an emergency procedure to manage severe hemorrhagic shock from torso injury but can cause severe ischemia of the lower extremities. However, lower extremity ischemia occurring as a complication of REBOA has been rarely reported. We describe the severe lower extremity ischemia caused by REBOA with a 12-Fr sheath in a small-built patient. METHODS The patient was a 16-year-old male who developed severe hemorrhagic shock due to abdominal blunt trauma. Following REBOA with a 12-Fr sheath on the right femoral artery, an emergency laparotomy and angiography to control the hemorrhage were performed. Twenty-eight hours after admission, suspecting lower extremity ischemia and compartment syndrome, we removed the sheath with a manual maneuver and performed fasciotomy. The limb ischemia was thus partially resolved. However, amputation was necessary because of ischemic necrosis on day 32. Our patient was physically small, and the diameter of his femoral artery on the contralateral site of sheath placement was also small. Therefore, disproportion of the sheath and femoral artery sizes may have caused the ischemic complication. CONCLUSIONS Our experience highlights the importance of appropriate size selection for the sheath in line with the target vessel. We also recommend postoperative monitoring of limb perfusion in such cases with the use of near-infrared spectroscopy to facilitate the early detection of ischemia.