A 16-day-old girl who had not yet returned to her birth weight was brought to the emergency department with lethargy. She had tachypnea and marked hepatomegaly with a hepatic bruit, as well as eight small hemangiomas on the scalp, thorax, abdomen, and limbs that had been noted within days after birth. Abdominal ultrasonography showed numerous rounded hypoechoic lesions in the liver (Panel A). Whole-body magnetic resonance imaging showed contrast-enhancing hepatic lesions, as large as 20 mm in diameter, that were hyperintense on T2-weighted images (Panel B), a finding consistent with infantile hepatic hemangiomas. Moderate cardiomegaly was also noted. Laboratory studies showed a thyrotropin level of 25.5 mIU per liter (reference range, 0.50 to 8.50) and a reverse triiodothyronine level of greater than 3696 pmol per liter (reference range, 140 to 540). Complications of infantile hepatic hemangiomas include high-output cardiac failure, consumptive hypothyroidism, and bleeding. These vascular lesions typically have rapid growth followed by a phase of slow involution, sometimes over a period of years. Treatment with propranolol, furosemide, and high-dose levothyroxine was initiated. The liver lesions gradually reduced in size, and after 9 months, treatment was stopped successfully.