Nine case of a distinctive soft tissue tumor of the female pelvis and perineum are described. They were characterized by their occurrence in young women (ages 21-38), large size (up to 60 X 20 cm), locally infiltrative nature, and grossly gelatinous appearance. The initial clinical impression was usually that of a Bartholin gland cyst. The microscopic appearance was that of spindle or stellate cells widely separated by a loose myxoid stroma focally rich in collagen fibrils, a prominent vascular component, including many large thick-walled vessels without an arborizing pattern, and foci of proliferating glandular elements in two cases. Mitotic activity was exceedingly low. Ultrastructural study of the spindle cells showed features consistent with myofibroblastic differentiation. Four patients developed large local recurrences; one tumor recurred twice, 14 and 15 years after initial excision. No distant metastases have been documented to date, and all patients are alive and well. The differential diagnosis of this unusual tumor includes myxoma, myxoid liposarcoma, sarcoma botryoides, myxoid variant of malignant fibrous histiocytoma, nerve sheath myxoma, and other soft tissue tumors with secondary myxoid changes. We have chosen the term "aggressive angiomyxoma" for this neoplasm to emphasize the neoplastic nature of the blood vessels and its locally infiltrative and recurrent nature.