Background <p>The lumbar sympathetic nerve block stands as a pivotal approach in managing complex regional pain syndrome (CRPS) in the lower limbs. Retroperitoneal hemorrhage is an extremely rare and severe complication of lumbar sympathetic nerve block. Here, we report for the first time a case of retroperitoneal hemorrhage that initially presented with symptoms of femoral nerve compression.</p> Case presentation <p>An 81-year-old elderly female was diagnosed with CRPS. After undergoing an ultrasound-guided lumbar sympathetic nerve block at our hospital, discomfort in her right lower back was experienced, followed by stabbing pain, numbness in the anterior thigh, and significant lower limb movement impairment. We considered that the femoral nerve might be compressed by a hematoma or abscess. An emergency percutaneous drainage was performed, resulting in partial symptom relief. However, two days later, signs of hemorrhagic shock were observed in the patient. An emergency lumbar arterial embolization was performed, effectively stabilizing her vital signs. One week later, lower limb pain and numbness disappeared, and right lower limb motor function fully recovered.</p> Conclusions <p>When retroperitoneal hemorrhage is suspected, prompt computed tomography (CT) or bedside ultrasound should be conducted. Once imaging supports the diagnosis, immediate digital subtraction angiography (DSA) could be utilized to identify the bleeding source and conduct embolization.</p>