People infected with HIV are now living longer and healthier lives than HIV-infected people of previous generations because of the widespread use of HAART medications. However, as HIV infection becomes a more chronic illness, rather than a fatal disease, researchers are beginning to identify the long-term complications of HIV infection and its treatment. Adults infected with HIV are increasingly developing the following: hyperlipidemia and dyslipidemia, both of which are associated with high cholesterol levels; endothelial dysfunction; insulin resistance; and changes in body composition, including increased obesity levels and an increase in central body fat. These conditions are all associated with an increased risk of cardiovascular disease. More research is needed to examine how children infected with HIV who are receiving HAART may be affected by these conditions. In this study, researchers will examine children infected with HIV who are receiving HAART (as well as a control group of children who are not infected with HIV) to evaluate vascular function and inflammation over time and how they affect body composition, fat redistribution, insulin resistance, hyperlipidemia, growth, nutrition, bone metabolism, and disease severity. This study will also evaluate the effectiveness of an exercise program on vascular function and cardiovascular outcomes in children infected with HIV who are receiving HAART.