MicroRNAs (miRNAs) represent a group of small, non-coding RNA molecules that have been shown to regulate gene expression at the translational level by interfering with the 3’ untranslated region of messenger RNAs. Gene silencing through miRNA interference is one epigenetic mechanism impacting the development and homeostasis of the organism. MiRNAs are critical for regulation of several biological processes, cellular function, the cell cycle, differentiation and apoptosis. Deregulation of miRNAs was confirmed in several pathologies including cancer (in lung cancer among others), asthma, COPD, diabetes and cardiovascular diseases. In mice models of asthma it has been found that increased levels of miR-21 and miR-126, and decreased levels of miR-672 and miR-143 are associated with regulation of cytokines involved in inflammation and remodeling, namely Il-13, Il-12, Il-10 and matrix metalloproteinase-12 (MMP-12). In lung cancer, overexpression of several miRNAs (miR-155, miR21, miR-17-92, miR221/222) and downregulation of let-7, miR-1, miR-29 and miR-126 has been found. It has been shown that serum miRNA profile may be regarded as a potential tool for early, non-invasive lung cancer diagnosis, and it can be used for chemotherapy sensitivity prediction and prognosis. MiRNAs seem to represent a promising goal in the search for new biomarkers and may be considered as an interesting target for therapeutical intervention.