Abstract: Recently discovered microRNAs (miRNAs) are a class of small RNA molecules that regulate gene expression at the post-transcriptional level. A large body of evidence implicates aberrant miRNA expression in most human malignancies. miRNAs are involved in many cellular processes that are altered in carcinogenesis, such as differentiation, proliferation and apoptosis. We review the role of miRNAs in the development and progression of cancer and their potential value in the diagnosis, treatment, and prognosis of cancer.