Cutaneous deciduosis is an exceedingly rare manifestation of endometriosis potentially mistaken for malignancy and thus far documented solely within surgical scars. We describe two additional cases, one occurring in a pregnant 21-year-old woman as a solitary flat erythematous vulvar papule, an extraordinary location not previously recorded. Histologic examination in that case revealed a subepithelial nodular aggregate of atypical large dyscohesive cells with accompanying edema and inflammation. An immunohistochemical panel showed positivity of the cells for vimentin and Ki-1 (CD30). Intracellular sulfated mucin and glycogen were also demonstrated. In a second case, a 27-year-old woman had a nodule at the umbilicus, removed incidentally during the course of cesarean section. Microscopically there were several circumscribed, multilobulated, intradermal nodules with variably sized lumens formed by crowded large epithelioid cells. The disparate histologic appearance of these examples highlights an essential challenge in their diagnosis. Clinical recognition is difficult unless suggested by more characteristic history or location. (J Am Acad Dermatol 2000;43:102-7.)