Lymphatic disorders may be challenging to diagnose because of the limited number of cases and diversity of symptoms. Along with the clarification of pathogenesis, advancements in diagnostic nomenclature and scrutinized internationally standardized classifications have been observed. Several causal genes have been elucidated and included in the classification system. The International Society for the Study of Vascular Anomalies (ISSVA) has established a classification of lymphatic disorders. For example, simple vascular malformations (IIa) or Lymphatic Malformations (LMs) include Generalized Lymphatic Anomaly (GLA), Kaposiform Lymphangiomatosis (KLA), and Gorham– Stout Disease (GSD). Morbidity and mortality of LMs are induced by infection or significant compression of the circulatory, respiratory, and digestive organs. To relieve symptoms, pleurodesis and sclerotherapy may be effective in providing local control. However, complete surgical extirpation of all lesions is considered risky due to adhesions around vital organs, such as the lung and mediastinal large vessels. Thus, the role of surgery remains unclear. In patients with GLA, the disease-causing genes identified from endothelial cells have a somatic mutation in neuroblastoma RAS. Other genes such as PIK3CAm were advocated as causal genes of another subset of LMs. Therapeutic agents are being developed based on these germlines and somatic mutations.