Edema is defined as an excess of interstitial fluids. Its appearance is always linked to a relative functional insufficiency of the lymphatic drainage, but the use of the word lymphedema is restricted to the conditions where the lymphatic insufficiency is the primary pathogenetic factor of edema formation. The lymphatic insufficiency may result from: 1) an incompetence of the lymphatic capillaries, either due to their aplasia (Milroy's disease) or to their destruction (lipodermatosclerosis of chronic venous insufficiency); 2) an insufficiency of the lymphatic collectors related to their hypoplasia (primary lymphedema), or their destruction by trauma, infection or carcinologic treatments; a drug related functional insufficiency of lymphatic collectors is probable, but more data are needed on this topic; 3) pathologic lymphatic nodes (surgical excision, invasion by hematological disorders or cancer) could interfere with their ability to concentrate lymphatic fluids. Local tissue changes in the lymphedematous limbs are important and should be taken into account in the care management of such patients.