Stewart-Treves syndrome (STS) is a rare but aggressive upper extremity lymphangiosarcoma in postmastectomy patients. Unfamiliarity with this disease and the innocuous appearance of the tumor often lead to delayed diagnosis. A comprehensive search of the databases at a single tertiary-care academic institution revealed only 3 cases of STS in the last 63 years. The latency time between breast cancer treatment and diagnosis of STS was 11 to 21 years. Survival after diagnosis of STS ranged from 8 to 15 months. One patient underwent radical surgery. The extensive lymphangiosarcoma in the other 2 patients precluded surgical resection and they underwent chemotherapy. All patients had adjuvant radiation therapy at the time of the original breast cancer resection. This report includes a discussion of the epidemiology, etiology, presentation, treatment, and prognosis of STS.