Fifteen ovarian malignant mixed müllerian tumors (MMMT) of the ovary are reported in an attempt to identify morphologic factors of prognostic interest. Several features were correlated to survival: histologic subtype and nuclear and histologic grades of the epithelial component; histologic subtype, grade, and mitotic rate of the mesenchymal component; necrosis and epithelial-to-mesenchymal ratio. The epithelial component was mainly of endometrioid (four cases) and serous (four cases) types. The mesenchymal component was largely heterologous, of which five were of chondromatous and five of rhabdomyoblastic differentiation. This latter differentiation was further demonstrated by electron microscopy (two cases) and immunohistochemistry (four cases). Ten tumors showed hyaline droplets that stained for α1-antitrypsin in two cases. Eight patients died of their disease, 13 days to 32 months after diagnosis (median, 5 months). Seven were alive 3 to 49 months (median, 10 months) after initial therapy. No morphologic factor was found to correlate with survival, but a tendency was observed for ovarian MMMTs with a high epithelial nuclear grade, a predominance of the mesenchymal component, or a rhabdomyoblastic mesenchymal component to be associated with more aggressive behavior. The histologic appearance of metastases did not correlate with prognosis.