The Stewart-Treves syndrome was first described in 1948, it's an angiosarcoma developed on a longstanding lymphadenomatous limb, more often after radical mastectomy. Diagnosis is made on skin biopsy and the prognosis is poor when radical surgery can't be performed. We report the case on a Stewart-Treves syndrome in a sixty-six years old woman who underwent radical mastectomy for breast carcinoma ten years earlier. Surgery was not feasible at the time of diagnosis, and we lost touch of the patient even if chemotherapy was decided. Radical surgery is the best treatment to date for this rare disease. Conservative surgery with adjuvant radiotherapy is also possible. Systemic chemotherapy is reserved for locally advanced unresectable and metastatic forms. We advocate long term follow-up for every post mastectomy lymphedema to diagnosis this fatal disease when curable.