MicroRNAs (miRNAs) are small non-coding ribonucleic acids (RNAs) consisting of approximately 22 nucleotides which are believed to control posttranscriptional gene expression by targeting messenger RNA (mRNA) either by degradation or silencing. This article focuses on the importance of miRNAs in different diseases. There are observations or even evidence that miRNA is involved in the pathogenesis of diseases such as autoimmune, cancer, cardio-vascular, metabolic and infectious diseases. The manipulation of the expression of one or several specific miRNAs could prove to be a promising treatment option, and may improve diagnostics and therapeutics in future patient care.