Diffuse angiomatosis of the extremities is a rare condition characterized by extensive or multifocal benign mass-forming vascular lesions involving multiple tissue planes; histologically, adipose and fibrous tissue are admixed with vascular elements that vary from capillary proliferations to large vessels that are often structurally abnormal. Although diffuse angiomatosis most likely represents a hamartomatous form of arteriovenous malformation, it behaves clinically as a benign but slowly progressive and unresectable neoplasm. We describe a case of diffuse angiomatosis of the lower extremity that presented clinically as a soft-tissue sarcoma.