Limb lymphedema is frequent and not well-known. Clinical classification distinguishes primary lymphedemas due to developmental disorders of the lymphatic system (hereditary or not, sometimes associated with other malformations) and secondary lymphedemas. Primary lymphedema is a lymphedema without a cause to explain lymphatic impairment. It is due to an abnormal lymphangiogenesis in utero. It is often associated with mutation in a gene involved in lymphangiogenesis (FOX C2, VEGFR 3, SOX18, PROX 1…). To assess clinical diagnosis, non-invasive techniques are able to study structure and function of the lymphatic system (mainly isotopic lymphography). Treatment is the complex decongestive therapy which associates manual lymphatic drainage and bandage. Predisposing or precipitating factors have to be treated (particularly streptococcal infections). Surgical treatment has precise and rare indication.