Non-random, specific chromosome aberrations can be found by direct preparation in the karyotype of the malignant cell populations of the various leukemias and solid tumors in childhood. These chromosomal deletions in neuroblastoma, Wilms-Tumor, reticlassification and prognosis. There are mainly chromosomal deletions in neuroblastoma, Wilms-Tumor, retinoblastoma whereas translocations predominate in leukemias and lymphomas.