Oncogenesis is correlated with the occurrence of multiple genomic events allowing cancer cells to acquire new properties, including the capacity of survival and proliferation with down regulated control signals. Among those genomic events, the study of recurrent translocations, particularly common in oncohematology, has allowed for a better understanding of leucemogenesis and lymphomagenesis mechanisms. These translocations are classically distinguished depending on their physiopathologic consequences. It may encode for a fusion gene leading to a chimeric protein, which exhibits a new activity or an aberrant one, corresponding in most cases to the constitutive activation of a proto-oncogene. In other cases, these translocations may cause abnormal expression of a proto-oncogene with a regular structure by a transcriptional deregulation. Beyond this highlighting recurrent translocations and understanding better the physiopathologic consequences of these chromosomal modifications has a real impact on patients. These cytogenetic anomalies represent an essential diagnostic tool for some hematologies; and pave the way for a better evaluation of the prognosis and thus, a better adaptation of the therapeutic strategy. They also contributed to improve survival with the development of targeted therapies. Finally, thanks to cytogenetic techniques combined to molecular biology techniques, cytogenetic aberrations can be used as a marker of response, which allowed a monitoring of residual disease.