A 73-year-old man visited our hospital because of right anterior chest pain. Computed tomography of the chest revealed an irregular mass in the anterior right upper lobe, along with rib destruction and osteolytic changes in the second thoracic vertebra. After 16 days, he noted gradually increasing back pain. After 25 days, he visited the emergency department because of paraplegia and urinary retention. Magnetic resonance imaging of the spine was performed. The sagittal T1- and T2-weighted images revealed a ventral subdural hematoma with cord compression, presenting as T1 hypo- to isointense and T2 hyperintense signals. On the same day, an urgent laminectomy was performed, and the subdural hematoma was removed. The postoperative course was uneventful and the paraplegia resolved. Eventually a diagnosis of acute spinal subdural hematoma because of thoracic vertebral metastasis of squamous cell lung cancer was made.