A 77-year-old woman was referred for evaluation of fingertip ulcers. She had arteriovenous malformation of the left arm (Panel A) that had been present since childhood. Physical examination revealed hypertrophy, with a giant arteriovenous malformation involving her fingers, forearm, elbow, and upper arm. The malformation was pulsatile, with dilated veins and arteries, and a palpable thrill. Small ulcerations were noted in the fingertips. There was no indication of cardiac failure. A magnetic resonance angiogram of the elbow, forearm, and hand (Panel B, dorsal view, three-dimensional, maximum-intensity projection) showed enlarged and tortuous arteries and veins, with several sites of aneurysmal dilatation throughout the imaged portion of the limb (Panel B, arrow) and multiple high-flow arteriovenous shunts. Parkes Weber syndrome consists of venous and capillary malformations and high-flow arteriovenous shunts, with overgrowth of the affected limb. Most cases are sporadic, although the syndrome may be inherited. Some cases are caused by mutations in RASA1. The syndrome rarely appears in the arm, particularly with this degree of vascular dilatation, which is presumably the result of lifelong evolution. It is more common for the legs to be affected. The patient did not want surgical treatment, and the ulcers are being managed with compressive therapy and local wound care.