Inflammation of the lymphatic vessels. It may be acute or chronic, it may affect superficial (superficial lymphangitis) or deep (deep lymphangitis) lymphatics, or have a reticular involvement, when the network of dermal lymphatics is affected (in which case it is also called acute erysipeloid lymphangitis, owing to its similarities to erysipelas); or with truncular involvement, when mostly the major lymphatic trunks are affected. From an etiopathogenetic point of view, several causes may trigger lymphangitis: infections are for sure the most frequent one, especially those due to streptococci (beta-hemolytic group A Streptococcus), staphylococci (Staphylococcus aureus), coli, and pneumococci. However, lymphangitis pictures can sometimes be observed after traumas, or in association with systemic inflammatory lesions (e.g. in rheumatic diseases). The immune system of the extremity affected by lymph stasis is somehow “deficient”, not so much because of cell impairment – as is the case in systemic immunodeficiency -, but rather because some of the cells in charge of providing adequate immune response (e.g. macrophages, Langerhans cells, or, more generally APC, that is Antigen Presenting Cells) are unable to move about properly. For this reason, a small lesion (such as an insect bite) is sufficient to let saprophyte germs in, thus triggering a lymphangitis episode. From a clinical point of view, lymphangitis may present some severe clinical problems. Indeed, depending on the type of germs that have penetrated into the body, on their bacterial load, and on any local immunodeficiency of the affected individual, even severely acute episodes may take place, in some cases leading to overt septicaemia and life-threatening conditions, which require hospitalization of the patient to an intensive-care unit for proper monitoring of the patient’s vital parameters. More commonly, acute lymphangitis presents with a picture of erythema involving the affected extremity, featuring all the five semeiotic parameters linked to inflammation (rubor, calor, dolor, tumor and laesa functio), associated with hyperpyrexia, (up to 41°C axillary temperature with or without shivering). Antibiotic therapy associated with symptomatic therapy (pain killers, antipyretic drugs), administered during hospitalization of the patient, is so far the treatment of choice. In lymphedema patients or in patients with disorders associated with lymph stasis, antibiotic prophylaxis should be recommended, with slow-release penicillins (one i.m. injection every 2-3 weeks), in order to protect patients from this dangerous complication.