Prognostic factors in yolk sac tumors of the ovary. A clinicopathologic analysis of 29 cases. Twenty-nine ovarian cancer patients with yolk sac tumors and germ cell tumors with yolk sac tissue as a component of their disease (16 endodermal sinus tumor, 11 mixed germ cell tumors, one embryonal carcinoma, and one polyembryoma) were treated with cytoreductive surgery and combination chemotherapy. Prognostic factors were investigated in this group. Patients with Stage I disease had a more favorable prognosis (P less than 0.003) than those with Stages II and IV disease. The difference in prognosis was significant in cases where residual tumor was absent (P less than 0.003) and in cases where ascites was either absent or less than 100 ml in volume (P less than 0.05). Endodermal sinus tumor with either an intestinal (P less than 0.05) or microcystic pattern (P less than 0.01) was more common in survivors than in those who died. The age, preoperative serum alpha-fetoprotein level, maximum tumor size, and tumor weight had no significant correlation with prognosis. In advanced cases, chemotherapy regimens including cisplatin gave better results than those containing vincristine, dactinomycin, and cyclophosphamide (P less than 0.05). The optimal treatment of yolk sac tumors or tumors with yolk sac tissue as a component of the ovary is discussed in light of these results. 