P53: gene alterations correlate highly with advanced ovarian carcinoma in women. In mice, p53 deficiency predominantly results in the formation of lymphomas and sarcomas. However, ovarian epithelial tumors have not been documented in p53 homozygous mutant (p53-/-) mice, probably because they die before other tumors can form. To determine whether p53-/- ovaries can develop epithelial tumors, they were transplanted into the ovarian bursae of histocompatible wild-type recipient females. The p53-/- ovarian grafts formed tumors approximately 1 year post-transplantation. The tumor type was angiosarcoma, suggesting that vascular tissues are predisposed to tumor formation in p53-/-ovaries. These findings suggest that p53 deficiency alone is not sufficient for ovarian epithelial tumorigenesis in mice. Thus, other genetic lesions are likely required to develop mouse models of human ovarian cancer.