Lymphangiomatosis (recently renamed "generalized lymphatic anomaly") is a rare disease of unknown etiology that features an increase in the number of lymphatic vessels in many different tissues. Gorham-Stout disease(GSD) is a related disease characterized by lymphatic vessels involving the bones and resulting in progressive bone destruction. Respective definitions remain unclear because these conditions largely overlap in the clinical setting and are both associated with pleural effusion and other visceral lesions. These two conditions have recently been differentiated based on imaging findings. GSD is characterized by progressive osteolysis with loss of cortical bone. These diseases present considerable diagnostic and therapeutic challenges. Implementation of basic and clinical research is mandatory to improve understanding of these conditions and optimize management.