Hepatitis C is a major public health problem worldwide. Therapy of hepatitis C virus has improved after introduction of the pegylated interferon and ribavirin therapy, but till now there is a large number of non responders. In order to improve the response rate, many studies try to identify the risk factors that are associated with the poor response to therapy. It was found that hepatitis C infection was associated with insulin resistance and it is suggested that insulin resistance may affect the response to interferon therapy. This book therefore discuss whether insulin resistance and body mass index can affect the response to pegylated interferon plus ribavirin therapy.