<qa>  What is the main cause of mortality in HIVHCV co-infection?Since the introduction of highly active antiretroviral therapies HAART, liver disease secondary to HCV infection has become a leading cause of morbidity and mortality in HIVHCV co-infection. The influence of HCV co-infection on the progression of HIV has been less clear and the results have been conflicting. Studies conducted in the pre-HAART era did not find that HIVHCV co-infection influenced the progression of HIV-induced immunodeficiency or death. Of four large studies conducted after HAART was introduced, two suggested a faster progression of HIV disease in the presence of HCV co-infection and two found no influence of HCV co-infection on overall mortality or progression of HIV disease. HCV may also negatively influence HIV disease in indirect ways, such as making the discontinuation of antiretroviral treatment more frequent because of an increased risk of liver toxicity.The morbidity and mortality resulting from the rapid progression of HCV infection in HIV-co-infected patients, particularly given the advances in HIV treatment that have improved the life expectancy of HIV-infected patients, support treating HCV infection in these patients. 