With the development of new technologies in the diagnosis of leukemia, we have modified the method of approaching individual cases. In addition to morphological examination, cytochemistry, immunophenotyping, electron microscopy and cytogenetics are now routinely used for daily practice. Furthermore, various molecular diagnostic methods are being tested, and some are already being used for diagnostic processes. The new technologies have certainly changed the diagnostic approach. When the diagnosis is supported by such multiple diagnostic methods, it is more reliable, reproducible and standardized. The communication among clinical practitioners through accurate diagnosis is valuable from both the therapeutic and prognostic point of view. In this article, the diagnostic method of leukemia is reviewed with an emphasis on practical aspects. Individual details are beyond the scope of this article. Interested readers are referred to the bibliography for more in depth treatment of the various techniques.