COL109413 is a Phase IV retrospective database study involving the review of medical records of approximately 850 HIV-infected patients treated at a single center (Peabody Health Clinic, Dallas, Texas) and followed for up to a 4-year period (2003-2006). Patients whose GFR decreased >25% from baseline (BL) will be identified and their disease and treatment characteristics will be compared to those of patients whose GFR did not change. GFR will be calculated by both the MDRD and the Cockcroft-Gault methods.