PURPOSE The purpose of this study is to learn more about multifocal lymphangioendotheliomatosis with thrombocytopenia (MLT). MLT is a rare vascular disorder characterized by multiple congenital skin and visceral lesions, profound thrombocytopenia, and gastrointestinal bleeding. The skin lesions may appear red, brown or blue, often misdiagnosed as hemangiomas. The gastrointestinal tract, liver, and lungs are the most common internal organs involved. The severe thrombocytopenia (low platelets) is believed to be the result of platelet trapping within the skin and visceral vascular lesions. Severe and chronic gastrointestinal bleeding is common during infancy and early childhood. Although a relatively newly described entity, MLT was likely previously reported as hemangiomas, blue rubber bleb nevus syndrome, diffuse hemangiomatosis, Kasabach-Merritt phenomenon, and hereditary hemorrhagic telangiectasia. The term cutaneovisceral angiomatosis with thrombocytopenia is also a term used for this same disease. This study is a longitudinal cohort study of MLT to collect detailed clinical data on the distribution of disease, disease severity, and complications. This data will be used to create diagnostic criteria and an evaluation protocol for infants with this disease