A 35-year-old female drug addict developed a painful left supraclavicular swelling and profound left arm weakness associated with left hand paresthesia and swelling after cocaine injection into the left base of her neck. Arteriogram confirmed a 3.7-cm false aneurysm of the left subclavian artery and a filling defect of the proximal left axillary artery. Emergent intraoperative treatment consisted of false aneurysm resection, embolectomy, and placement of a prosthetic graft. Distal circulation was restored, but the neurological deficit persisted in the left arm and a fever developed in the patient, necessitating rehospitalization 3 weeks after discharge. False aneurysm, a vascular complication of parenteral drug abuse, may lead precipitously to death by exsanguination if not efficiently and effectively diagnosed and treated.