Carcinosarcomas of the female genital tract have generally been regarded as a type of sarcoma. Recent evidence suggests, however, that they may be more closely related to carcinoma. The histologic features of 29 carcinosarcomas with documented metastases were analyzed to study the relative importance of the carcinomatous and sarcomatous components and attempt to provide further evidence on the histogenesis of these neoplasms. Patients' ages ranged from 33 to 81 years (mean, 68). The primary tumor originated in the uterus in 17 cases, the ovary in 11, and the fallopian tube in one. Heterologous sarcoma was present in 21 of the primary tumors (72%). Myometrial invasion was present in all 15 of the uterine tumors treated with hysterectomy and consisted only of the carcinomatous component in 12 cases (80%). In two cases, which possibly developed as "collision"-type carcinosarcomas, the myometrium was separately invaded by carcinoma and sarcoma. Myoinvasive tumor consisted solely of sarcoma in one case. Lymphatic-vascular invasion was found in 10 of the primary tumors (eight uterine, two extrauterine) and consisted of pure carcinoma in all instances. The cellular composition of 62 metastases was evaluated. Of these, 51 metastases were diagnosed concurrently with the primary tumor in 21 patients (73%). Eleven metastases were diagnosed from 2 to 26 months after initial treatment. Carcinoma only was found in 43 metastases (70%), both carcinoma and sarcoma in 15 (24%), and sarcoma alone in four (6%). A total of 35 lymph node metastases occurred in 10 cases, consisting of carcinoma alone at 34 sites. The sole example of a purely sarcomatous lymph node metastasis occurred in one of the possible uterine "collision"-type tumors. Intraperitoneal metastases to serosal surfaces or the omentum occurred in 19 cases and consisted of both carcinoma and sarcoma in 14 and carcinoma only in five. Vaginal metastases occurred in four cases and consisted of only carcinoma in two, carcinoma and sarcoma in one and only sarcoma in one. Four patients had distant organ metastases, including one each to the liver (carcinoma only), breast (carcinoma only), bone marrow (sarcoma only), and brain (sarcoma only). Of the 51 concurrent metastases, only carcinoma was present in 37 (73%), both carcinoma and sarcoma in 13 (26%), and sarcoma alone in one. Of the 11 subsequent metastases, carcinoma alone was found in six (55%), sarcoma alone in three (27%), and both carcinoma and sarcoma in two (18%).(ABSTRACT TRUNCATED AT 400 WORDS)