The morphological features of a retroperitoneal teratoma in a 10-month-old girl are reported. Unlike the usual pattern of the teratoma, this tumor was composed predominantly of nephroblastomatous tissue. Histologically, glomeruloid and tubular structures were identified in nests of undifferentiated blastemal elements. Hyaline cartilage, adipose tissue, glial tissue and glands lined by mucin-secreting columnar epithelium were minor elements. A focal cystic structure lined by thin flattened epithelium was also noted. Retroperitoneal teratoma with predominance of nephroblastic elements is of interest not only because of its rarity but also because it needs to be differentiated from extrarenal Wilms' tumor, since both of these tumors have different origins.