Thoracic disc herniation is less common rather than cervical or lumbar herniation. Cases of sudden onset without trauma are especially rare. Generally, the neurological onset of disc herniation is caused by mechanical cord compression due to a protruded disc, and its onset is usually gradual. Ischemia is also considered as a factor of neurological onset. We report a case of a 78-year-old male with sudden paraplegia while straining at the toilet. T2 weighted MR image on admission showed mild disc protrusion at the level of Th8-9 and intramedullary high signal intensity below the Th8-9 level. We speculate that Valsalva-like maneuver had led to the congestion of vertebral venous plexus or compression of the anterior spinal artery, and spinal ischemia occurred.