Lymphangioleiomyomatosis (LAM) is a rare disease usually occurring in young women of child-bearing age. It is characterized by a distinctive proliferation of lymphatic smooth muscle cells, especially occurring in the pulmonary parenchyme. The majority of primary LAM occurs in the lung, but there are a few reports of extrapulmonary cases. We report a case of a 21-yr-old female who first complained of low abdominal pain and was referred from a local clinic with the impression of an ovarian cyst. Gynecologic ultrasonography revealed a large posterior pelvic mass with an irregular echogenicity measuring 9.7 x 4.2 cm in size. Pelviscopy showed a large, thin walled, partly cystic, pelvic mass. The mass was partly removed. Microscopically, the mass was characterized by a haphazard proliferation of smooth muscle cells arranged in fascicular, trabecular, and papillary patterns around a ramifying network of endothelium-lined spaces. The cells were plump or epithelioid with abundant eosinophilic cytoplasm and showed a positive reaction for both alpha-smooth muscle actin and HMB-45 antigen. Surgical and pathological findings were consistent with pelvic retroperitoneal LAM. Despite the numerous treatment attempts, the patient suffered from intractable chylous ascites and developed pulmonary LAM and died due to severe respiratory distress.