Three benign mesoblastic nephroma cases aged 10 days, 14 months and five years are presented. A comparative histological study of the tumors with a review of the literature suggested that they are essentially benign and may be considered mesenchymal tumors, similar to those seen in older age groups and probably differing only in size and in the age-dependent retained differential potentiality of the metanephric blastema of very young children. The unique association of neurofibromatosis in one of these cases suggested some relationship between the neural crest and mesenchyma in very young children. Although biologically different, mesoblastic nephroma may be one of the congeners of Wilms' tumor, not a hamartoma.

Keywords: congenital tumor, hamartoma, kidney tumor, mesoblastic nephroma