The authors studied a rare, congenital, cutaneous vascular anomaly that grows proportionately with the child and does not regress. A total of 53 patients were compiled from three vascular anomaly centers. These patients' lesions were analyzed for presentation, physical findings, radiologic and histopathologic characteristics, natural history, and outcome after resection. The lesions occurred slightly more often in male patients, always appeared alone, and were located (in order of frequency) in the head/neck region, extremities, and trunk. They were round-to-ovoid in shape, were plaque-like or bossed, occurred in variable shades of pink to purple, and had an average diameter of 5 cm. The overlying skin was frequently punctuated by coarse telangiectasia, often with central or peripheral pallor. The lesions were warm on palpation; fast-flow was further documented by Doppler ultrasonography. Magnetic resonance imaging and angiographic findings were similar to those of common hemangioma of infancy. All lesions were easily excised without recurrence.Histologic examination revealed lobular collections of small, thin-walled vessels with a large, often stellate, central vessel. Interlobular areas contained predominantly dilated, often dysplastic veins; arteries were also increased in number. Small arteries were observed "shunting" directly into lobular vessels or into abnormal extralobular veins. "Hobnailed" endothelial cells lined the small intralobular vessels. Mast cells were increased. Tests for glucose transporter-1, a recently reported reliable marker for common hemangioma of infancy, were negative in all 26 specimens examined. In conclusion, the authors think these clinicopathologic and radiologic features define a rare vascular lesion for which the term "noninvoluting congenital hemangioma" is proposed. These lesions of intrauterine onset may be a variant of common hemangioma of infancy or another hemangiomatous entity with persistent fast-flow.