The objective of this subanalysis of the Phase III DUET trials was to examine virological response to an etravirine-containing regimen in patients harbouring virus fully sensitive to etravirine. Full etravirine sensitivity was defined as fold change in 50% effective concentration (FC) ≤3 or weighted genotypic score ≤2. At Week 48 in the etravirine group, 74% of patients with etravirine FC ≤3 and 77% with etravirine genotypic score ≤2 had viral load <50 HIV-1 RNA copies/mL, versus 48% and 46%, respectively, in the placebo group (P < 0.0001). Response rates increased with baseline phenotypic sensitivity score, but were consistently higher with etravirine (56-82%) than placebo (2-72%). Similar observations were made in patients harbouring virus with full etravirine and darunavir sensitivity. Our findings support current recommendations to include three active agents in treatment-experienced patients' regimens.