Immunophenotyping by flow cytometry has become indispensable for the diagnosis of hematopoietic neoplasms.  More recently, post-therapeutic monitoring of residual disease has become increasingly recognized as one of the most important measures of clinical response in patients with acute leukemia and is rapidly becoming standard of care in pediatric B-lymphoblastic leukemia.  In parallel, molecular techniques such as next generation sequencing have also been developed that allow post-therapeutic monitoring of residual disease.  This talk will describe the current approaches used for the diagnosis and monitoring of acute leukemia by flow cytometry and describe their relative merits relative to next generation sequencing  for the monitoring of acute leukemia.