Spontaneous intracranial hypotension (SIH) is believed to be a benign disease. However, numerous studies have reported serious complications related to SIH, including subdural hematoma. In this case report, a 54- year-old male patient visited the emergency room with orthostatic headache. A brain magnetic resonance imaging (MRI) study showed diffuse mild thickening and enhancement of pachymeninges, with a suspicious minimal amount of subdural fluid collected in the left posterior parietal area. His orthostatic headache showed no improvement with conservative treatment; but his pain was almost completely relieved after two trials of cervical epidural blood patch. On the 74th day after the onset of his pain, the patient showed a drowsy mental status and slurred speech when he visited the pain clinic. Brain computerized tomography indicated a left subdural hemorrhage, and he underwent emergency operation to drain the SDH. In conclusion, pain clinicians should pay attention to abrupt changes in mental status as well as continuous headache, for the early diagnosis of SDH in SIH patients.