Detectable karyotypic changes have been observed in more than 50% of the patients with ALL, distinct nonrandom chromosome abnormalities have been found. Some of these can be correlated with particular parameters such as age, morphology of the blasts, lymphocyte surface markers, prognosis. Karyotype is an important independent prognostic factor in ALL, even when other well-known risk factors are considered but an abnormal clone is not always associated with a poor prognosis. Burkitt leukemia and lymphomas have been shown to present characteristic and specific translocations t(8;14) and variants t(2;8) and t(8;22). It appears that the structural change of chromosome no 8 involving band q24 is a consistent chromosome feature in these malignancies, and that this peculiar region on chromosome no 8 probably plays an important biological role in the development of these malignant proliferations. The association of cytogenetic and molecular biology techniques would allow in the near future a better understanding of the genesis and significance of chromosome anomalies in malignant blood diseases.