Flow cytometry is one of the key technologies for acute leukemia (AL) diagnostics. Nevertheless, lack of technological standards hampers implementation of immunophenotyping data in treatment protocols. Earlier our group published the acute lymphoblastic leukemia diagnostic standards. In this paper, we present the updated guidelines for initial immunophenotyping of ALs. This wellharmonized approach includes recommendations for monoclonal antibodies choice, sample preparation, cytometer setup, data analysis and interpretation as well as for the report writing. These guidelines allows application of diagnostic flow cytometric studies in all types of AL.