Background: Long-term (96-week) efficacy and safety of the protease inhibitor (PI) darunavir coadministered with low-dose ritonavir (DRV/r) was evaluated in HIV type-1 (HIV-1)-infected patients with extensive prior treatment experience in the POWER 1, 2 and 3 trials. Methods: Patients with HIV-1 RNA≥1,000 copies/ml and ≥1 primary PI mutation were randomized to receive either DRV/r 600/100 mg twice daily plus an optimized background regimen (OBR), or an investigator-selected control PI (CPI) plus OBR (POWER 3 was a DRV/r 600/100 mg twice daily single-arm study). The proportion of patients with HIV-1 RNA<50 copies/ml at week 96 was assessed (intent-to-treat [ITT], time-to-loss of virological response algorithm). Results: In total, 467 patients received DRV/r 600/100 mg twice daily; 124 patients received CPI(s). At week 96, 39% of DRV/r patients in POWER 1 and 2 (pooled analysis) versus 9% of CPI patients achieved HIV-1 RNA<50 copies/ ml (ITT, time-to-loss of virological response algorithm; P<0.001). A similar proportion of DRV/r patients (42%) in POWER 3 achieved HIV-1 RNA<50 copies/ml at week 96. Mean absolute CD4+ T-cell count increase for DRV/r at 96 weeks was 133 cells/mm3 in POWER 1 and 2 and 103 cells/mm3 in POWER 3. Grade 2-4 treatmentemergent adverse events at least possibly related to DRV/r (≥2% incidence, excluding laboratory abnormalities) were diarrhoea (3%), vomiting (3%), nausea (2%) and headache (2%). Conclusions: Treatment with DRV/r 600/100 mg twice daily was well tolerated and led to sustained virological and immunological responses in treatment-experienced HIV-1-infected patients over 96 weeks.