Lymphangiosarcoma in dogs, an extremely rare tumour with only 16 cases reported in the literature, is reviewed. Lymphangiosarcoma in humans, also very rare, and known in post-mastectomy, chronically-lymphoedematous patients as 'Stewart-Treves' syndrome, is briefly outlined, as well as the various other causes of lymphoedema, both primary and secondary, which usually precede malignancy. Comparisons between human and canine lymphoedema are made when such references were found. The genetic links to primary lymphoedema and the manifestation thereof in humans are mentioned. Lymphangiosarcoma in the majority of human and canine patients is an aggressively malignant tumour with few patients surviving despite various attempted treatments. The tumour most commonly arises in the subcutaneous tissues and rapidly invades underlying tissues and may spread widely internally via haematogenous and lymphatic routes, with frequent pleural and chest involvement. The tumour has been reported mostly in medium- to large-breed dogs, in slightly more males than females, and in an age-range of 8 weeks to 13 years, with more cases aged 5 years and older. Methods of diagnosis, with the variations encountered, including routine histopathology, immunohistochemistry, electron microscopy, tissue culture characteristics and endothelial expression of glycocongugates, are discussed.