This project will identify all patients who have a laboratory-confirmed diagnosis of Hepatitis C. The intervention group will be those who had a prescription filled for a new antiviral medication after October 10, 2014, and who were naive to treatment for Hep C prior to the prescription. The comparison group will be those who have not been treated for Hep C. Incidence of the following types of adverse events will be measured: acute or acute-on-chronic or uncertain cause liver failure (including liver transplant), acute kidney failure, myocardial infarction, liver cancer, multiple organ failure, stroke, and death. For liver failure in particular, a chart review will be conducted to validate the outcome. The initial analysis will use a Poisson model that includes exposure time (time to adverse event or censoring event). Other analytic methods may be employed to address channeling by indication.