The three-direct-acting antiviral (3D) regimen containing ombitasvir, paritaprevir, ritonavir, and dasabuvir with or without ribavirin (RBV) is approved for treatment of hepatitis C virus (HCV) genotype 1 (GT1)/human immunodeficiency virus type 1 (HIV-1) coinfection. Results of a pharmacokinetic substudy of 3D and darunavir are presented. HCV/HIV-1-coinfected subjects were randomized to maintain an antiretroviral regimen with darunavir at 800 mg once daily (QD) or switched to a regimen with darunavir at 600 mg twice daily (BID). On study day 1, subjects received 3D and RBV plus darunavir for 12 weeks. Pharmacokinetic parameters were compared for darunavir and ritonavir with and without 3D (week 4 and day -1). Pharmacokinetic parameters of 3D were compared to historical data. Ten subjects received darunavir QD, and 12 subjects received darunavir BID. The central value ratios (90% confidence interval [CI]) for maximum concentrations (Cmax), area under the plasma concentration-time curve between 0 and 24 h postdose (AUC24), and trough plasma concentration at 24 h postdose (C24) of darunavir administered QD with 3D versus administration of darunavir alone were 0.92 (0.72, 1.18), 0.83 (0.71, 0.98), and 0.64 (0.44, 0.93), respectively. The ratios (90% CI) for darunavir Cmax, AUC12, and C12 administered BID with 3D were 0.92 (0.76, 1.12), 0.88 (0.73, 1.05), and 0.73 (0.58, 0.92), respectively. Exposures of 3D were similar to or slightly lower than those in historical data. All darunavir trough concentrations (Ctrough) associated with an HIV-1 RNA level of >40 copies/ml were above the darunavir 50% effective concentration (EC50) of 550 ng/ml for resistant virus. In conclusion, the 3D regimen with darunavir QD or BID did not affect darunavir Cmax and AUC, whereas the darunavir Ctrough decreased. Changes in pharmacokinetic parameters of 3D were not considered clinically significant. Episodes of intermittent HIV-1 viremia were infrequent and were not associated with darunavir Ctrough values below 550 ng/ml. (This study has been registered at ClinicalTrials.gov under identifier NCT01939197.).