Treatment of hepatitis C virus (HCV) infection has progressed considerably with the approval of interferon-free, direct-acting antiviral (DAA)-based combination therapies. Although most treated patients achieve virological cure, HCV resistance to DAAs has an important role in the failure of interferon-free treatment regimens. The presence of viral variants resistant to NS5A inhibitors at baseline is associated with lower rates of virological cure in certain groups of patients, such as those with genotype 1a or 3 HCV, those with cirrhosis, and/or prior nonresponders to pegylated interferon–based regimens.