We present a rare case of traumatic acute subdural hematoma (SDH) in which intracranial hypotension (IC) secondary to cerebrospinal fluid (CSF) leakage at the lumbar spine caused delayed neurological deterioration. A 70-year-old male sustained a head injury after ground-level fall and was brought to our institution. A brain computed tomography (CT) showed a thin acute SDH with mild brain shift, and conservative management was initiated. He exhibited neurological deterioration on the 9th hospital day, however, and a brain CT showed a change in CT density and marked an increase in hematoma volume and brain shift. It was thought that conversion from acute to subacute SDH was associated with the deterioration, and emergency hematoma evacuation was performed. Despite the surgery, neither clinical nor radiographical improvement occurred. The lack of improvement pointed to the presence of underlying IC, and a CT myelography revealed the dural sleeve of the right L2 nerve root as the source of the CSF leakage. An epidural blood patch therapy was performed on the 12th hospital day to seal the CSF leakage. The postprocedural course was uneventful, and the patient was discharged free of symptoms on the 20th hospital day. Spinal CSF leakage should be considered as a cause of delayed neurological deterioration in patients with traumatic acute SDH which exhibits conversion to subacute SDH.