The paper describes 2 cases of immature ovarian teratoma with elements of nephroblastoma (ICD-0 code 9080/3) in patients aged 61 and 70 years. Microscopic examination revealed that both cases had blastemal cells with scant cytoplasm and basophil nuclei sticking together. Epidermal, glandular, rhabdomyoblastic, chondroid, bone, neuroectodermal, and histiocytic components were determined. Papillary and glomeruloid structures and primitive tubules were immured in the sarcomatous stroma. Immunohistochemical studies showed a strong reaction with Wilms tumor 1 (WT1), paired box gene (PAX-2), cytokeratin 7, desmin, smooth muscle actin, and α-1 antitrypsin. The recurrent tumors displayed a 1.8- to 6.1-fold increase in the level of p53. At the same time, the molecular genetic study revealed p53 gene mutation. In both cases, serous ovarian cystadenocarcinoma was misdiagnosed, ineffective chemotherapy was performed, and a recurrence occurred. The literature review revealed only 8 such cases.