A case of endometrial stromal sarcoma (ESS) showed cystic pulmonary metastases mimicking lymphangiomyomatosis (LAM). A 58-year-old female, who had undergone total hysterectomy for low-grade ESS 16 years previously, had repeated bouts of pneumothorax. Multiple thin-walled cysts in the peripheral lung were revealed by radiological examinations. In an open-lung biopsy specimen, cystic lesions were surrounded by layers of spindle-shaped cells of varying thickness that resembled LAM. However, in addition to subtle histologic differences from LAM, HMB45 (antimelanoma antibody) showed positive in LAM (n = 3), but was negative in ESS (n = 2) and the cystic lesions of this case. Using myogenic markers (desmin and alpha-smooth muscle actin), metastatic ESS could be immunohistochemically differentiated from mesenchymal cystic hamartoma (n = 1). HMB45 immunohistochemistry is useful in the differential diagnosis of cystic pulmonary lesions.