A 19-year-old man was admitted with the chief complaint of a sudden onset of thoracic pain and paraplegia. His right lower limb had progressively enlarged since he was 3 months old. Transient paraparesis had occurred recurrently since the age of 3. Physical examination on admission revealed that there were multiple warts on his face, trunk and right extremities. The right lower limb was thicker and longer than the left one, and the temperature was 1 degree C higher in the right side. Neurological examination revealed paraplegia and severe impairment of all sensory modalities below Th4 with bilateral clonus. Radiological examination showed lordosis of the thoracic spines with thinning of the pedicles of Th4 to Th6. Selective spinal angiography showed a juvenile type of arteriovenous malformation involving the cord of Th2 to Th6 with multiple feeding arteries, and a glomus type of the lower thoracic cord with the feeding arteries from Adamkiewicz's artery and the right Th10 intercostal artery. MRI showed the cord enlargement of Th2 to Th6 and within it the nidus was identified. Spinal arteriovenous malformations associated with Klippel-Trénaunay-Weber syndrome were noticed. The patient underwent interruption of the main feeding artery and removal of the dilated vessels located in the dorsum of the thoracic cord. Postoperative course was uneventful with slight improvement of clinical symptoms. Klippel-Trénaunay-Weber syndrome is manifested by a triad of symptoms: 1) hemihypertrophy of the extremities, 2) cutaneous hemangiomas and 3) arteriovenous fistula or varicose veins of the involved limbs. Nineteen cases of Klippel-Trénaunay-Weber syndrome associated with spinal arteriovenous malformation have been reported. The pathogenesis has been suggested to be due to developmental abnormalities.