Magnetic resonance (MR) imaging findings of two patients with Stewart-Treves syndrome are presented. MR imaging showed edematous changes in the subcutaneous fat and skin masses that proved to be angiosarcomas. MR signal intensity of the tumor was low compared with fat on T1-weighted images and intermediate and heterogeneous on T2-weighted images. In one patient, administration of intravenous Gd-DTPA showed marked enhancement in the early phase, which persisted until the delayed phase. These finding on dynamic MR imaging may reflect the abundant vascular spaces seen in these tumors.