A nontraumatic spontaneous spinal acute subdural hematoma (sSDH) is a rare complication after spinal surgery. Although an sSDH is often associated with anticoagulation therapy, vascular malformations, or lumbar puncture, the pathogenesis of nontraumatic spontaneous sSDH remains unclear. We present the case of an intradural hematoma after an extraforaminal surgery through the Wiltse approach for an extraforaminal disk herniation at L5/S1. This 58-year-old woman experienced hypoesthesia and progressive motor dysfunction in the left leg several hours postoperation. Urgent magnetic resonance imaging revealed an intradural hematoma at the L1/L2 to L2/L3 level in the ventral dural sac proximal to the surgical level. Surgical decompression was performed. There was no evidence of trauma, coagulopathy, or anticoagulation therapy. To our knowledge, this case is the first to report an acute sSDH proximal to the surgery level after an extraforaminal spinal surgery through the Wiltse approach for an extraforaminal disk herniation. It illustrates that attentive postoperative neurologic monitoring, even in the absence of intraoperative irregularities, remains important to diagnose and treat this complication at the early stage.Thieme. All rights reserved.