MicroRNAs (miRNAs) are small non-coding RNAs involved in the regulation of critical cell processes such as apoptosis, cell proliferation and differentiation. A small set of miRNAs is differentially expressed in hematopoietic cells and seemingly has an important role in granulopoiesis and lineage differentiation. In this study, we analysed, using a quantitative real-time PCR approach, the expression of 12 granulocytic differentiation signature miRNAs in a cohort of acute promyelocytic leukemia (APL) patients. We found nine miRNAs overexpressed and three miRNAs (miR-107,-342 and let-7c) downregulated in APL blasts as compared with normal promyelocytes differentiated in vitro from CD34 progenitors. Patients successfully treated with all-trans-retinoic acid (ATRA) and chemotherapy showed downregulation of miR-181b and upregulation of miR-15b,-16,-107,-223,-342 and let-7c. We further investigated whether the APL-associated oncogene, promyelocytic leukemia gene (PML)/retinoic acid receptor α (RARα), might be involved in the transcriptional repression of miR-107,-342 and let-7c. We found that PML/RARα binds the regulatory sequences of the intragenic miR-342 and let-7c. In addition, we observed, in response to ATRA, the release of PML/RARα paralleled by their transcriptional activation, together with their host genes, EVL and C21orf34α. In conclusion, we show that a small subset of miRNAs is differentially expressed in APL and modulated by ATRA-based treatment. © 2009 Macmillan Publishers Limited All rights reserved.