This study will include two populations of patients. Patients in Population A are on stable HAART that includes TDF and will either be in Group I (compensated liver disease) or Group II (decompensated liver disease). All patients in Population A will be randomly assigned to one of two arms: Arm 1 patients will receive 10 mg ADV daily and TDF placebo; Arm 2 patients will receive ADV placebo and 300 mg TDF. Patients in Population B are on stable HAART and have never taken TDF as part of their HAART. Population B patients will receive 300 mg TDF daily during the course of the study.