BACKGROUND: Breast cancer-related lymphedema is an unsolved iatrogenic dilemma. Disfigurement of the affected limb because of increased volume and recurrent cellulitis can cause both physical and mental distress for many breast cancer survivors. No adequate animal models have been developed to investigate acquired lymphedema mimicking breast cancer-related lymphedema, and there is little knowledge of the anatomy of the lymphatics in animals. The authors hypothesized that a canine forelimb model of the lymphatic system could potentially be used to study breast cancer-related lymphedema. METHODS: Six forequarters were used from three mongrel hound carcasses. The lymphatic microinjection technique used hydrogen peroxide to identify lymphatic vessels. The individual channels were injected with a radiopaque lead oxide mixture and recorded on digital radiography. Lymphatic territories (lymphosomes) in the canine forelimb were demarcated and color coded in accordance with their lymph nodes. The lymphatic system in the canine forelimb was compared with that in the human upper extremity. RESULTS: The lymphatic system in the canine forelimb was divided into two superficial lymphosomes (ventral cervical and axillary) and one deep lymphatic system. The ventral cervical lymphosome was larger than the axillary lymphosome. A single lymph node in the axilla received fluid from three sites: the ventral cranial torso, the superficial medial forelimb, and the deep forelimb. The lymphatic systems of the human upper extremity and the canine forelimb had some anatomical similarities: distinct superficial and deep system and size of the lymphatic vessel. CONCLUSION: The canine model may be a valuable animal model for investigating the pathophysiology of upper extremity lymphedema.