Hemangiomas are the most common congenital lesions in childhood. They are generally superficial tumors and cause a red or violet color change on overlying skin. Most of them gradually regress by time, and become nearly imperceptible before puberty, but some bigger and deeper lesions tend to persist in adult life. Although some genetic disorders like von Hippel-Lindau syndrome are known to be closely associated with multiple hemangiomas (hemangiomatosis), most of them are sporadic and the etiologic factors have not been clearly elucidated. The liver and spleen are two internal organs which can be involved by hemangiomas. Although hemangiomas are generally harmless lesions, local or systemic unwanted effects can sometimes be seen. Rupture and bleeding caused by rapid enlargement, and hematological manifestations primarily appearing as thrombocytopenia, anemia, and coagulopathy may be cited as examples of serious complications. The latter clinicopathologic condition is manifested by hemorrhagic diathesis and is known as Kasabach-Merritt syndrome. The mortality rate is reported to reach one third of the affected patients.