Background We report a case of a 71-year-old woman diagnosed with Stewart-Treves syndrome, a rare occurrence after breast cancer treatment. Methods The patient, with a history of cancer in the left breast, was subjected to radical mastectomy with regional lymph node dissection, radiation and chemotherapy in 1985. In 2009, the patient presented with a 4 months history of enlarging plaques of purplish maculae and nodules in the area of chronic lymphedema. A skin biopsy was performed. Serial sections from the material were stained with HE Ki67 positivity was 60-65% and ACT was positive in vessels. The clinical and pathologic features confirmed the diagnosis of Stewart-Treves syndrome. The patient was treated with radiotherapy and remission of all cutaneous lesions of the arm was obtained. Conclusions Treatment of post-mastectomy lymphangiosarcoma is still unsatisfactory, since this tumor develops in long-standing chronic lymphedema many years after the initial surgery, long term follow-up of patients with chronic lymphedema is required.