In the last decade our understanding of acute promyelocytic leukemia (APL) has advanced tremendously. The recognition of all-trans retinoic acid (ATRA) as a powerful therapeutic agent paralleled the cloning of the t(15;17) breakpoint. RtPCR for the PML-RARA hybrid mRNA has become the hallmark of molecular diagnosis and molecular monitoring in APL. Current techniques are useful in predicting complete remission and a possible cure in many patients who repeatedly test negative by PCR. Standardizing techniques and improving the sensitivity of the assay are important. Doing this in a way so that clinically relevant minimal residual disease can be distinguished from "indolent disease" remains among the future challenges in APL.