Faldaprevir is a potent hepatitis C virus (HCV) NS3/4A protease inhibitor and an inhibitor of UDP-glucuronosyltransferase-1A1 (UGT1A1), which is involved in raltegravir clearance. Raltegravir, an HIV integrase inhibitor, may be used in combination with HCV treatment in HCV/HIV co-infected patients. In this open-label, 2-period, fixed-sequence study, 24 healthy volunteers (12 males) received faldaprevir 240 mg and raltegravir 400 mg in 2 treatment schedules (A and B) separated by a washout phase of ≥7 days: (A) twice-daily raltegravir (Days 1–3), once-daily raltegravir (Day 4); (B) twice-daily raltegravir and twice-daily faldaprevir (loading dose, Day 1), twice-daily raltegravir and once-daily faldaprevir (Days 2–5), once-daily raltegravir and once-daily faldaprevir (Day 6). Pharmacokinetics and safety were assessed over 132 hours post-dosing. Compared with raltegravir alone, co-administration with faldaprevir led to 2.7-fold and 2.5-fold increases in raltegravir geometric mean AUCτ,ss and Cmax,ss, respectively, and a similar increase in raltegravir glucuronide metabolite exposure. No serious adverse events (AEs) were reported and no subject discontinued due to AEs. Faldaprevir and raltegravir co-administration was well tolerated and resulted in a moderate increase in raltegravir exposure.