The anomalous retro-psoas iliac artery is an extremely rare congenital iliolumbar vascular anomaly. A 51-year-old woman presented to our emergency department with worsening right lower extremity pain and weakness for 3 months. CT angiography of the right lower extremity showed no evidence of stenosis in the lower extremity arteries and the incidental finding of an anomalous right retro-psoas iliac artery. Herein, we report a rare case of anomalous retro-psoas iliac artery. Surgeons and clinicians need to be aware of this rare congenital anomaly to avoid severe complications during pelvic or orthopedic surgery.