Lower back pain commonly develops following spinal anesthesia. This pain is likely caused by strain on the ligaments associated with paraspinous muscle relaxation and positioning during the operation. We describe a case involving a healthy 61-year-old woman with a varicose vein that was scheduled for phlebotomy under spinal anesthesia. Two days after spinal anesthesia, the patient experienced severe lower back pain that was markedly aggravated by twisting and extension of the spine, but subsided with rest. Immediately after a lumbar medial branch block was performed at the area of tenderness the pain subsided. Thease results suggest that immediate treatment of acute lower back pain is important for preventing progression to chronic low back pain.