The prime purpose of this article is to know about promyelocytic leukemia. Acute promyelocytic leukemia is an exclusive subordinate kind of the severe leukemias. It has distinct cytogenetics, clinical features, and biologic characteristics. APL is caused by an arrest of leukocyte differentiation at the promyelocyte stage. The discovery and elucidation of the molecular pathogenesis for APL has led to the first and only targeted therapy for leukemia.