Inclusion Criteria:  Patient 2 years of age and older Venous, lymphatic, or venolymphatic malformations  Exclusion Criteria:  Children with contraindication to use of sirolimus Children with history of transplant Children with a history of natural immunodeficiency Children with a history of artificially induced immunodeficiency Children with a history of a serious or life-threatening infection Children taking CYP3A4 inhibiting medications Children taking strong CYP3A4 inducers to avoid subtherapeutic dosing/exposure. Inability or unwillingness of subject or legal guardian/representative to give informed consent Women that are or may become pregnant o Sirolimus is a Pregnancy Category C drug. No randomized controlled studies have been done on pregnant women. Women of childbearing potential must be on effective contraception prior to, during, and for 12 weeks following sirolimus therapy.