The primary objective of this study is to compare the effectiveness of EFV-based regimens in HIV-1-infected patients who; (1) were previously allergic to NVP and stopped all ARV simultaneously; (2) were previously allergic to NVP and continued the other NRTIs for a period of time, i.e. "staggered interruption"; and (3) started EFV-based regimens as an initial regimen (as controlled group).