The pharmacokinetics of tenofovir, efavirenz and estradiol were determined in 20 HIV-infected transgender women receiving tenofovir-DF/emtricitabine/efavirenz (300/200/600 mg once daily) and feminizing hormone therapy (FHT; estradiol 2 mg/day and cyproterone 25 mg/day). Estradiol AUC, Cmax and C24 decreased by 28%, 19% and 36%, respectively, in the presence of ART. FHT had no significant effect on the pharmacokinetics of tenofovir (AUC, Cmax and C24 decreased by 14%, 7% and 17%, respectively) or efavirenz (AUC, Cmax and C24 decreased by 6%, 1% and 9%, respectively). Despite significant reductions in estradiol concentrations (likely due to enzyme induction by efavirenz), bioavailable testosterone levels were not increased in the presence of ART. Further studies should determine whether these reductions are clinically significant and whether they are replicated when other FHT or ART regimens are used.