Kaposi sarcoma is characterized by a proliferation of irregular jagged vascular channels, which partly surround preexisting blood vessels in some areas. This characteristic appearance of a small vessel protruding into an abnormal vascular space has been termed "promontory sign". Cutaneous angiosarcoma (AS) is a malignant vascular neoplasm comprised of a meshwork of anastomosing irregular dilated vessels between collagen bundles and around skin appendages, lined by atypical endothelial cells. The presence of promontory sign has not been described as a histologic finding in AS. We retrieved all cases of cutaneous AS from the files of Yale Dermatopathology Laboratory between 1990 and 2007. Sixty-six biopsies from 15 patients (7 men and 8 women) were reviewed. The lesions were divided histologically in a patch, plaque, or tumor stage according to the depth of invasion of malignant cells. Forty of the 66 biopsies were from a patch or plaque stage of AS. The remaining 26 biopsies were from tumor stage of AS. In 13 of 40 biopsies (32.5%) of patch and plaque lesions of AS, promontory sign was identified, seen primarily in the upper reticular dermis. These biopsies were taken from 11 patients (6 men and 5 women), ranging in age from 36 to 86 years (median 69). Promontory sign was not found in any of the 26 biopsies of tumor stage AS. The presence of promontory sign has not been emphasized in lesions other than Kaposi sarcoma, but seems to be a feature that is not uncommon in patch/plaque stage AS.