We report the cytogenetic findings observed in the cancer cells of a Wilms' tumor in a 11-month-old girl without the phenotype of the WAGR. Two populations were identified: one had a 46,XX,del(11)(p11p13) karyotype and the other had a translocation involving the deleted chromosome 11 and chromosome 12, t(11;12)(p11;q13). This result strongly suggests that the deletion of 11p was the initiating event to the tumor and that the translocation has been instrumental in promoting its development.