An intraspinal vascular malformation associated with the Klippel-Trenaunay-Weber (KTW) syndrome initially was thought to be intramedullary on angiographic findings. Postmortem examination revealed an entirely posterior extramedullary arteriovenous fistula (AVF) fed by the anterior spinal artery. The association of the KTW syndrome with a so-called intramedullary AVF has been described in the literature without any pathologic confirmation (11 cases). Our case emphasizes the difficulty of determining the exact morphology and location of spinal AVF on arteriography. The association of the KTW syndrome with a retromedullary AVF can be explained on a developmental basis.