The biological classification system provides a useful clinical distinction between proliferative and biologically stable vascular anomalies. Hemangiomas demonstrate the ability to proliferate, then involute, and the majority still are followed conservatively. Intervention usually is reserved for life- or vision-threatening lesions. Surgical reconstruction may be indicated for the 10% to 30% of hemangiomas that do not regress adequately. The use of lasers to treat early hemangiomas is controversial but may gain greater clinical application as favorable data accumulate. In the future, biological suppression with antiangiogenic agents may become the preferred mode of therapy. Vascular malformations represent developmental errors in embryogenesis. They are present at birth, do not proliferate, and do not regress spontaneously. Lasers, interventional radiology, and surgical therapy may offer significant palliation and possible cures. It is important that the physician understand the difference between these two groups to better provide appropriate prognostic and therapeutic advice to the parents of children with these anomalies.