In its classical form, embryonal rhabdomyosarcoma (ERMS, botryoid type) is a vaginal neoplasm occurring in infants and young girls and is often not considered in the differential diagnosis of uterine corpus and cervical spindle cell tumors in adult women. Clinicopathologic and immunohistochemical features of 25 cases of ERMS in women 20 years of age or older were analyzed. Patient age ranged from 20 to 89 years (mean, 44.4 y; median, 46 y), with 8 patients aged 20 to 39 years, 14 patients aged 40 to 59 years, and 3 patients older than 60 years of age. Tumors originated in the cervix in 20 cases and in the uterine corpus in 5. They were characterized by an edematous hypocellular spindle cell proliferation, typically with cellular condensation beneath epithelial surfaces (cambium layer), in which tightly packed hypercellular foci were scattered. Neoplastic cells had hyperchromatic nuclei and minimal cytoplasm, usually with delicate cytoplasmic processes. Occasionally, elongated or globular cells with eosinophilic cytoplasm (rhabdomyoblasts) were evident, but cytoplasmic cross-striations were only rarely identified. Apoptotic bodies and mitotic figures were usually identified in the hypercellular foci. Hemorrhage was common, often making recognition of the hypercellular foci difficult. Desmin and myogenin were coexpressed in 22 of 23 (95.6%) tumors evaluated. Proliferative activity, as assessed by Ki-67 expression, was notably elevated in all tumors evaluated, typically concentrated in the hypercellular foci. Estrogen and progesterone receptors were expressed focally in only 3 of 12 (25%) and 1 of 8 (12.5%) tumors evaluated, respectively. Follow-up was available in 7 cases. Five patients were alive without evidence of disease with follow-up of 3 to 8 years, and 1 patient was alive with disease at 5 months. One patient died at 5 months with pulmonary nodules, but it was not determined whether this was due to metastatic ERMS or the patient's known ductal breast carcinoma. ERMS has a broader clinical profile than classically expected and should be considered in the differential diagnosis of a uterine corpus or cervical spindle cell tumor, regardless of patient age. Recognition can be rendered difficult by the hypocellular background, which can suggest a benign polyp or low-grade tumor, and hemorrhage, which can obscure the characteristic hypercellular foci. Identification of hypercellular foci in which mitotic activity and apoptotic bodies are found, desmin and myogenin are coexpressed, proliferative activity is notably elevated, and hormone receptor expression is usually absent is very useful for establishing the diagnosis.