Spontaneous retroperitoneal hematomas are a rare yet potentially devastating occurrence associated with antiplatelet and anticoagulant therapies. We present a case of a spontaneous retroperitoneal hematoma post-operatively after a total hip arthroplasty surgery performed under a midline approach spinal anesthetic. A 79-year-old male with a BMI of 25.72 kg/m2presented for anterior total hip arthroplasty. A midline approach with an uncomplicated spinal anesthetic was performed. On the night of postoperative day 0, the patient received a prophylactic dose of dalteparin. The patient reported back pain, contralateral leg numbness, and weakness that began overnight on postoperative day 0. A computed tomography (CT) scan confirmed a 10 cm, contralateral retroperitoneal hematoma. The patient underwent interventional radiology embolization followed by surgical evacuation and demonstrated improvement in the neurologic function of his affected leg. Despite the rarity of a spontaneous retroperitoneal hematoma formation in the perioperative period, it could be simultaneously evaluated when performing an MRI to rule out spinal hematoma if a patient suffers a post-op neurologic deficit after a neuraxial technique. Understanding the evaluation and timely treatment of patients at risk for a perioperative retroperitoneal hematoma could help clinicians prevent a permanent neurologic deficit.