A 43-year-old woman had unilateral exophthalmos caused by primary orbital E
wing sarcoma. Specialized immunohistochemical stains, primarily MIC-2 (CD99
), aided in the diagnosis of Ewing sarcoma. Twenty-two months after radioth
erapy and multiagent chemotherapy, the patient remained tumor free. To our
knowledge, this is the first reported case of orbital Ewing sarcoma to pres
ent in an adult beyond the fourth decade of life.