OBJECTIVES: This study examined trends in Medicare Part D plans' coverage of single ingredient and combination HIV ARV drugs; analyzed trends in cost sharing, premiums, and deductibles; and evaluated restrictions set by drug plans on HIV ARV drugs. METHODS: Data were obtained from the Centers for Medicare and Medicaid Services Prescription Drug Plan Formulary and Pharmacy Network Files for the month of December for the year 2005-2015. Information for each plan included: dosage forms, active ingredients (single or fixed-dose combination) formulary information (coverage, prior authorization, specialty tier), and cost-sharing structure (coinsurance or copayment). Descriptive statistics were conducted. RESULTS: The study included 37 HIV ARV drugs marketed in the US in the period 2006- 2015. There were 10 fixed-dose combination HIV ARV drugs and 27 single active ingredient HIV ARV drugs. There were 3 drugs subject to prior authorization and 1 drug subject to step-therapy during part of the study period. The median quantity limit ranged from 26.8 to 31.9 days. Most formulary plans required patients to pay co-insurance instead of copayments for covered HIV ARV drugs. The use of specialty tiers (tiers 4-6) increased during the study period. The percentage of formularies using tier 5 for at least 1 HIV ARV drug was 1.6% in 2006 and 13.6% in 2015. CONCLUSIONS: Part D plans covered all HIV ARV drugs marketed in the US in the period of 2006- 2015. Prior authorization or step therapy requirements were not common restrictions to access to HIV ARV drugs. Conversely, quantity limit days were common restrictions in drug coverage. Most plans required patients to pay a coinsurance and a higer percentage of HIV ARV drugs were placed in specialty tiers.