The development of various analitic techniques like classical cytogenetics, molecular cytogenetics and molecular methods has greatly improved our ability to understand the basis of cancer development, that can be helpful in hematological diagnostics and treatment. Thus, improving these methods and raising the diagnostic standards remain of key importance in haematooncology. The influence of cytogenetic and biomolecular analysies on clinical decisions has increased considerably recently, but laboratory techniques have to be optimized to provide reliable results for the best patient care. The aim of this study is to present the basis of genetic diagnostic methods used in hematooncology and their role in clinical practice.