During the past 10 years, 25 infants with alarming hemangiomas--lesions that impaired important functions and were life threatening, especially when there was visceral involvement--have been treated. A vascular mark was present at birth in 68% of these infants. Visceral hemangiomas were associated with bulky cervicocephalic hemangiomas or with small hemangiomas scattered over the body. Among the 25 infants, 12 had laryngeal hemangiomas, 3 had hepatic hemangiomas, and 1 had gastrointestinal hemangiomatosis. Ocular sequelae, malocclusion, and cutaneous distortion were the most important functional problems. Corticosteroid treatment was used for 23 of 25 infants with alarming hemangiomas. There was a varied treatment response: total failure (30% of the patients); excellent, dramatic, rapid improvement (30% of the patients); and moderate, doubtful response, with the natural course of the disease remaining unaltered (40% of the infants). Arterial embolization, used in 6 infants, gave inconstant results. Cardiac failure, frequently associated with large cutaneous hemangiomas and always seen with hepatic multinodular hemangiomas, required digitalization. In some cases arterial embolization reduced the increased cardiac output. Liver hemangiomas had a high mortality; all 3 infants with hepatic involvement died.