Infantile hemangioma (IH) is the most common tumor of infancy. Although its biologic properties are still quite mysterious, its clinical characteristics are for the most part well delineated. Thus, we know that a typical hemangioma will grow rapidly during infancy followed by a gradual involution. Most IHs will grow for about 6 months. As a consequence, clinical treatment is conservative, and intervention is usually reserved for IHs that threaten organ function (eg, those with intraorbital growth). Because medical treatment involves drugs such as methylprednisolone or interferon alfa, clinicians are usually not too keen on intervening unless they really have to. In a number of cases, growth will be prolonged. If this occurs near vital structures, it might become a problem and would be a good indication for early intervention. Unfortunately, at present there is not a reliable set of criteria to help us decide which IHs will show prolonged growth and which will not.