Hobnail hemangioma, also known as "targetoid hemosiderotic hemangioma", represents a distinctive benign vascular tumor, characterized histologically by a biphasic growth pattern of dilated vascular structures lined by prominent hobnail endothelial cells in the superficial dermis, and collagen dissection by angulated vessels in deeper parts of the lesion. It is important to distinguish this tumor from patch stage Kaposi's sarcoma, retiform hemangioendothelioma and progressive lymphangioma. We report a 26-year-old man showing typical clinical and histological features of hobnail hemangioma. (Korean J Dermatol 2001;39(10): 1144-1147)