© The Author 2017. Published by Oxford University Press for the Infectious Diseases Society of America. All rights reserved. Background. Ombitasvir/paritaprevir/ritonavir with dasabuvir (OBV/PTV/r + DSV) ± ribavirin (RBV) is approved for hepatitis C virus (HCV) genotype 1 (GT1) treatment in HIV-1 coinfected patients. In healthy controls, coadministration of OBV/PTV/r + DSV + darunavir (DRV) lowered DRV trough concentration (Ctrough) levels. To assess the clinical significance of this change, TURQUOISE-I, Part 1b, evaluated the efficacy and safety of OBV/PTV/r + DSV + RBV in coinfected patients on stable, DRVcontaining antiretroviral therapy (ART). Methods. Patients were HCV treatment-naive or interferon-experienced, had CD4+ lymphocyte count >200 cells/μL or >14%, and plasma HIV-1 RNA suppression on once-daily (QD) DRV-containing ART at screening. Patients were randomized to maintain DRV 800 mg QD or switch to twice-daily (BID) DRV 600 mg; all received OBV/PTV/r + DSV + RBV for 12 weeks. Results. Twenty-two patients were enrolled and achieved SVR12. No adverse events led to discontinuation. Coadministration had minimal impact on DRV maximum observed plasma concentration and area under the curve; DRV Ctrough levels were slightly lower with DRV QD and BID. No patient experienced plasma HIV-1 RNA ≥200 copies/mL during treatment. Conclusions. HCV GT1/HIV-1 coinfected patients on stable DRV-containing ART achieved 100% SVR12 while maintaining plasma HIV-1 RNA suppression. Despite DRV exposure changes, episodes of intermittent HIV-1 viremia were infrequent.