Twelve women with mixed mesodermal tumors of the ovary were studied. These tumors grow rapidly and patients are frequently in an advanced state of their disease when the diagnosis is made. In 10 individuals the initial complaint was either an abdominal mass or increasing abdominal girth. With one exception, the patients were postmenopausal. The most important prognostic criterion was the stage of the tumor at the time of the diagnosis. Of nine women with Stage III and IV disease, only one is well and free of disease. No pathologic features were uncovered which could be related to prognosis. Am J Surg Pathol 4: 37-42, 1980.