Nine vulvar and three vaginal angiomyofibroblastomas from patients 23 to 71 years of age (mean, 46 yr) were analyzed. The tumors were well circumscribed and ranged from 0.9 to 11 cm (average, 4.7 cm) in maximal dimension. On microscopic examination, they had hypercellular and hypocellular areas. The neoplastic cells were spindle-shaped, plasmacytoid, or epithelioid; a variable number were binucleated or multinucleated cells. A focal storiform pattern was present in one tumor, and, in one tumor, the neoplastic cells formed a collar around a central area of dense collagen. There was no significant nuclear atypia, and there was less than one mitotic figure per 10 high-power fields. The tumors contained small- to medium-sized blood vessels, which were characteristically thin walled and, occasionally, ectatic and branching. The stroma was edematous, separated collagen fibers and contained a variable number of inflammatory cells, especially lymphocytes and mast cells. Three vulvar tumors contained a variable amount of fat. Ultrastructural study of three tumors showed intracytoplasmic, dilated, rough endoplasmic reticulum, moderate numbers of pinocytotic vesicles, and numerous filaments without dense bodies; rare intercellular rudimentary junctions were identified. Eleven of 11 tumors were immunoreactive for vimentin, 11 of 12 for desmin, three of 11 for muscle actin, one of 12 for smooth muscle actin, and four of 12 for CD34. There was no staining for factor XIIIa, keratin, S100 protein, Leu-7, glial fibrillary acidic protein, or CD68. Follow-up revealed no recurrences or metastases. Angiomyofibroblastoma is a distinctive benign tumor that arises most commonly in the vulva and vagina and has a diverse histologic and immunohistochemical profile.