The anatomy of the canine distal ulna was evaluated to determine its potential as a free vascularized bone graft. Twelve cadavers were studied by gross dissection and nonselective and selective angiography. The caudal interosseous artery consistently served as a source artery to the distal ulnar periosteal vasculature in all dogs. The diameters of the caudal interosseous artery and venae comitantes were large enough to permit microvascular anastomoses. Nonselective perfusions of the brachial artery demonstrated large barium-filled vessels within soft tissues surrounding the ulna with anastomotic connections between medullary and periosteal vasculature. Grafts selectively perfused through the caudal interosseous artery (periosteal circulation only) had barium-filled vessels within the muscular cuff, periosteum, cortical bone, and medullary canal of the ulna. A surgical approach to remove the distal ulna along with an intact musculoperiosteal cuff and its associated vasculature is described.