['The purpose of this study was to identify prostate cancer (PC) oncogenic microRNAs (miRs) based on miR microarray and to investigate whether these oncogenic miRs may be useful as PC biomarkers.', 'Initially, we carried out miR microarray and real-time PCR using RWPE-1, PC-3, DU-145 and LNCaP cells. To investigate the function of miR-183, we used a miR-183 knockdown inhibitor in cell growth and wound-healing assays. We used several algorithms and confirmed that they are directly regulated by miR-183.', 'We identified three potential oncogenic miRs (miR-146a, miR-183 and miR-767-5P). The expression of miR-183 in PC cells (PC-3, DU-145 and LNCaP) was upregulated compared with RWPE-1 cells. MiR-183 expression was also significantly higher in PC tissues compared with that in matched normal prostate tissues. Additionally, miR-183 expression was correlated with higher prostate-specific antigen, higher pT and shorter overall survival. MiR-183 knockdown decreased cell growth and motility in PC cells and significantly decreased prostate tumour growth in in vivo nude mice experiments. We identified Dkk-3 and SMAD4 as potential target genes of miR-183.'] Is microRNA-183 an oncogene targeting Dkk-3 and SMAD4 in prostate cancer?