In spite of the American Heart Association recommendations for blood pressure measurement, many physicians measure blood pressure in only one arm that is easy to access at the time of measurement. This practice can lead to incorrect management with significant interarm blood pressure difference. We report a case of a 51 years old man who was scheduled to undergo vascular bypass graft under combined spinal-epidural anesthesia. In 60 minutes after anesthesia, the blood pressure of left arm dropped from 110/65 mmHg to 74/45 mmHg. The blood pressure was still 80/50 mmHg after two injections of ephedrine. After checking radial pulse tone strength, we found significant interarm blood pressure difference. The blood pressure of right arm was 150/70 mmHg. Postoperative CT angiogram revealed significant stenotic portion in the left subclavian artery. This case emphasizes the importance of bilateral blood pressure measurement, especially in patients with peripheral vascular disease.