The improvement of the conventional cytogenetic techniques, the development of molecular cytogenetics and the application of techniques of molecular biology to genetic analysis have led to an authentic revolution in the knowledge of the processes implied in the development and progression of lymphoid neoplasias. In this way, a great part of the alterations present in malign cells have been characterised, and the genes involved in the transformative process have been established. This has important consequences for the clinical handling of this type of disease and makes possible a more exact diagnosis through a systematisation of the different entities based on their biological characteristics. On the other hand, the introduction of new techniques of analysis, such as real time PCR, will make it possible to monitor the disease quantitatively, making it possible to evaluate response to the different treatments and to establish predictive values for relapses. In the future, all of this knowledge will make it possible to establish genotype-specific therapies and to develop new medicines aimed at the alteration responsible for the malignant process and with less undesired collateral effects.