Patients who have previously received a first HIV NNRTI containing regimen or who have received an NNRTI containing treatment for prevention of mother to child transmission (MTCT), and who have never used a protease inhibitor (PI) may be eligible to participate. TMC125 (at 800 mg b.i.d. of the old formulation and after the formulation switch, 200 mg b.i.d. of the new formulation) will be studied versus an active control (investigator selected PI). All patients will receive an underlying therapy containing 2 investigator selected NRTIs. 300 patients will be enrolled in Argentina, Brazil, Mexico, Peru, Chile, Costa Rica, Russia, South-Africa, Spain, Thailand, UK, USA, Thailand, India and Malaysia. The duration of the study is 48 weeks with an optional extension for patients in the TMC125 treatment group until virologic failure or commercial availability of the drug. TMC125 at 800mg twice daily of the old formulation; after the formulation switch, TMC125 at 200mg twice daily of the new formulation. The initial duration is 48 weeks with an optional extension for patients in the TMC125 treatment group until virologic failure or commercially availability.