Intradural extramedullary cavernous malformations in the spinal cord are rarely occurring vascular lesions. Mostly they are clinically silent unless the hemorrhagic transformation causes subarachnoid hemorrhage or neurologic deficits. We report the case of a 51-year-old man who developed a headache and weakness of the lower limb. Spinal cord magnetic resonance imaging revealed that the cause of his symptoms was a spinal intradural and extramedullary cavernous malformation with hemorrhagic transformation causing subarachnoid hemorrhage and compression of the thoracic spinal cord. Surgical decompression of the spinal cord followed by the resection of the lesion resulted in significant neurological improvement. Early diagnosis and early surgical extirpation of the lesion should be done to prevent recurrent hemorrhagic transformation and development of neurological symptoms.