Grazoprevir is a second generation NS3/4A protease inhibitor approved in the EU and the USA for the treatment of hepatitis C virus (HCV) genotypes 1 and 4 infections in adult patients in combination with elbasvir (C virus (HCV) NS5A inhibitor) as the fixed-dose combination product Zepatier with or without ribavirin. In phase III trials, 12 or 16 weeks of treatment with once-daily elbasvir/grazoprevir (fixed-dose tablet or as individual agents), taken with or without ribavirin, generally provided high rates of sustained virological response at 12 weeks (SVR12) in treatment-naive and -experienced adult patients with chronic HCV genotype 1a, 1b or 4 infection, including those with or without compensated cirrhosis, HIV co-infection, inherited blood disorders or chronic kidney disease or patients receiving opioid agonist therapy or of Japanese origin. Elbasvir/grazoprevir was generally well tolerated. Thus, elbasvir/grazoprevir, with or without ribavirin, represents an effective new option for the treatment of adults with chronic HCV genotype 1 and 4 infection, including a number of difficult-to-treat populations.