MicroRNAs (miRNAs) are important post-transcriptional regulators of nearly every biological process in the cell and play key roles in the pathogenesis of human disease. As a result, there are many drug discovery programs that focus on developing miRNA-based therapeutics. The most advanced of these programs targets the liver-expressed miRNA-122 using the locked nucleic acid (LNA)–modified antisense oligonucleotide miravirsen. Here, we describe the discovery of miravirsen, which is currently in phase 2 clinical trials for treatment of hepatitis C virus (HCV) infection.