We report a case of an 11-year-old girl with a pulsatile mass in the thigh diagnosed by angiography as localized arteriovenous malformation. Recent increase in tenderness and size of the lesion brought the patient to hospital and excision was performed at the parents' request. Subsequent histologic examination revealed that this lesion was an alveolar soft-part sarcoma in disguise. The angiographic and pathologic results are presented. Other investigators should be aware of this uncommon and highly vascular sarcoma, which might be misdiagnosed as a localized arteriovenous malformation and thus treated only conservatively.