Lymphedema is the result of accumulation of protein-rich interstitial fluid (lymph stasis) caused by a failure of lymph drainage in the face of a normal capillary filtration. Whether the origin is congenital or acquired from infection, radiation, trauma, or surgery, chronic lymph stasis impairs local immune surveillance by disrupting trafficking of the immunocompetent cells in the lymphedematous district and stimulates vicarious angiogenesis by promoting development of a collateral lymphatic and hematic network in the lymphedematous district. When the local mechanisms of immune surveillance begin to fail, the lymphedematous region becomes an immunologically vulnerable area, predisposed to malignancy, chiefly vascular tumors such as Stewart-Treves syndrome and Kaposi's sarcoma, because of the continual angiogenic stimulus. (J Am Acad Dermatol 2002;47:124-7.)