The CTSI-PLACE Study is a study for men and women with HIV/hepatitis C co-infection or HIV only. The study looks at the impact of having hepatitis C virus in addition to HIV on risk for cardiovascular disease. Participants will undergo non-invasive assessment of cardiovascular disease risk through measurements of endothelial function and blood biomarkers at baseline and 1 year (or 4 weeks and 24 weeks after end of HCV treatment for those that undergo HCV treatment during study follow-up).