The standardization committee of the Korean Society for Laboratory Hematology revised laboratory testing guidelines in order that hematologic neoplasms could be diagnosed according to the revised 4th edition of WHO classification of tumors of haematopoietic and lymphoid tissues. The new guidelines were revised based on an extensive review of international guidelines that included the National Comprehensive Cancer Network Guidelines, and European LeukemiaNet recommendations that are based on the revised WHO classification. We expect that the newly revised guidelines will improve clinical decisions, standardize laboratory tests, and enhance the development of new molecular technologies that are integrated into diagnostic algorithms via ongoing consensus initiatives.