Mature microRNAs (miRNAs) are processed from non-functional (pre)-miRNAs by the enzyme Dicer. In this study, manipulation of Dicer level was used to explore the influence of miRNAs on cytotrophoblast proliferation in human placenta. Immunohistochemistry (IHC) showed Dicer in cytotrophoblast, but not in terminally differentiated syncytiotrophoblast. siRNA-mediated knockdown of Dicer was used to effect a global reduction in miRNA in first trimester placental explants, as a result of which cytotrophoblast proliferation was significantly enhanced. QPCR and IHC analysis following Dicer knockdown revealed that the expression of two nodal pro-mitogenic signalling molecules expressed within cytotrophoblast, ERK and SHP-2, was significantly enhanced. Studies are now required to identify individual miRNAs involved in regulating trophoblast proliferation. © 2012 Elsevier Ltd. All rights reserved.