The chronic lymphatic leukemia (CLL) is the most common form of leukemia in adults over 60 years, occurring approximately 5 to 30 new cases per year in each 100, 000 inhabitants.In the late 1970s, the cytogenetic study of this type of leukemia was rather inefficient, due to poor quantity and quality of the obtained metaphases.In following decade, it became possible to identify the most frequently encountered changes in this type of leukemia.However, even when metaphases with good quality were possible, only in 40 to 50% of all cases were detected ehromosomal abnormalities.Through the molecular cytogenetic (FISH), it became possible to detect alterations to 80%.With the faster and more accurate techniques, that have been available in this last years, it almost seemed as if the cytogeneties had fulfilled its function.However, as it happens frequently and in each scientific area, these new techniques have some limitations, particularly due to the fact that they are very targeted and still cause difficulties in interpretation.Indubitably, conventional cytogenetic has a low power of analysis, compared to other techniques; nevertheless, we must remember that this is our entire genomes first visualization.Experienced cytogeneticists, employing optimized protocols, are able to detect cytogenetic anomalies, associated to this type of leukaemia, which will definitely be important to the diagnosis and prognosis of the patient.Through a Research Project financed by the Portuguese Health State Department, the Oncotogic Centre and the Cytogenetic Laboratory of CHTMAD proceeded, together, to the identification by conventional cytogenetic and FISH of the most frequent genetic alterations in 50 patients with B-CLL not treated, in the region of Trás-os-Montes, and its correlation with the clinical data at diagnosis and time of progression to active disease.We have had success in the cellular culture in all the samples and it was possible to perform the cytogenetic and FISH analysis.The correlation of the cytogenetic results with clinical data is shown.The final report of this project is being prepared for publication.Concluding: classical cytogenetic plays a key role in the study of B-CLL, specially in order to enable the comprehensive evaluation of karyotype and identify the genetic changes with poor or good prognosis, as well as other cytogenetic changes that may exist.These results are of extreme importance both in the choice of therapy applied, in the monitoring of the diseases progression, and in the monitoring the minimal residual disease.