Fourteen patients with hemangiomas or arteriovenous malformations treated with operative management are described. Particular emphasis is placed on the definition of terms and the methods of differentiating arteriovenous fistulas, hemangiomas, and arteriovenous malformations. Arteriovenous fistulas are acquired lesions consisting of a single communication. Hemangiomas are congential lesions that rarely pulsate or have an associated bruit; moreover by angiography they have multiple small feeding arterial vessels and histologically are composed of numerous thin-walled, but normal-appearing, blood vessels. Arteriovenous malformations are also congenital but they pulsate and have associated bruits; furthermore on angiography they have a number of larger arterial feeding vessels and histologically are composed of abnormal dysplastic vessels. Operative management of all lesions should be carefully planned and executed. Arteriovenous malformations and skeletal muscle hemangiomas will have a tendency to recur if not completely excised.