Kasabach-Merritt phenomemon (KMP) is a profound thrombocytopenia resulting from intralesional platelet trapping. It is now clear that KMP occurs with KHE and tufted angioma, not with infantile or congenital hemangiomas. KMP is typically associated with more aggressive lesions and poorer outcomes. Clinically significant KMP is a severe thrombocytopenia, generally below 30× 109/L. Severe thrombocytopenia may indicate a severer tumor, a progressive tumor, partially or totally insensitive to therapy. In addition to severe, persistent thrombocytopenia characteristic of KMP, patients often manifest elevated D-dimer and low fibrinogen. Coagulopathy in addition to thrombocytopenia is associated with more aggressive presentations and may indicate current infection or inflammation. Additionally, KMP may be complicated by severe anemia due to blood sequestration and intra-lesional hemorrhaging. KHE with KMP have notably high morbidity and mortality rates, resulting predominantly from rapid tumor growth and infiltration, compression or destruction of vital structures, and hemodynamic instability.