A 50-year-old Korean man had an erythematous patch on the left side of his chest since birth (Fig. 1). We first regarded this lesion as nevus flammeus because of the resemblance of the lesion to an erythematous patch that blanched with pressure. Physical examination revealed an 8×5 cm erythematous patch with a central profuse sweating zone surrounded by a flame-like non-sweating zone (Fig. 2). The patch was sharply demarcated from the normal skin. Sweating was evoked by physical exercise or emotional stress. There was no history of pain or tenderness for the lesion. The patient had no history of any other vascular disease. Histopathologic examination of the central zone showed an increased number of eccrine glands in the mid and deep dermis. Some dilated vascular channels that were not associated with the eccrine glands were present in the upper dermis and subcutaneous tissue (Fig. 3). Immunohistochemical stain with anti-factor VIII-related antigen showed reactivity on the endothelia of the vascular elements which were not associated with eccrine glands in the upper dermis. Histopathologic examination of the surrounding zone showed nonspecific findings, except for the dilated vascular channels in the upper dermis.