Contrast-enhanced computed tomography (CT) revealed a multilocular cystic mass extending from the level of the renal artery origin to the internal and external iliac artery regions in a woman in her 40s who presented with vomiting and diarrhea. A percutaneous biopsy was performed, and histopathological examination revealed bundle-like proliferations of spindle-shaped cells with oval nuclei in acidophilic cytoplasm. Immunohistochemical staining was positive for HMB-45, alpha-smooth muscle actin, E-cadherin, and estrogen and progesterone receptors; the provisional diagnosis was perivascular epithelioid cell tumor. Considering the patient's age and sex, the final diagnosis was primary retroperitoneal lymphangioleiomyomatosis (LAM). She did not meet the diagnostic criteria for tuberous sclerosis complex and was considered to have sporadic LAM. As complete surgical resection was considered to be impossible and no lung lesions, which indicate poor prognosis, were observed, we decided to keep her under surveillance. The patient was asymptomatic, with no significant changes on imaging for 6 months.