This study describes various medication adherence patterns and SVR outcomes among treatment naïve, non-pregnant adult PWID enrolled in the HERO Study (a U.S. trial comparing modified DOT and patient navigation across eight opioid treatment programs and fifteen community health centers) who initiated sofosbuvir/velpatasvir (x12 weeks).  Electronic blister pack and SVR data were available for 496 participants, which comprised the per-protocol sample.  Adherence was summarized according to various patterns, such as total adherent days, consecutive missed/non-adherent days, and early discontinuations.  Multivariate models accounted for several factors including study site/setting, age, employment, injection frequency and recency, and urine drug screen results.  The median total adherent days was 63 (75%) per 84-day treatment course, and observed SVR rate was 460/496 (92.7%).  Participants with early or premature medication discontinuation (i.e., 1^st– and 2^nd-month discontinuation) were less likely to achieve SVR.  Participants who missed more than 14 consecutive adherent days had a significantly smaller chance of achieving SVR compared to people who missed ≤ 7 consecutive days (regardless of when it occurred).  Greater total adherent days were significantly associated with SVR only among the subgroup with < 50% adherence rate.  Overall, greater total adherent days, longer consecutive adherent days, and shorter consecutive missed days were all associated with 90% or higher SVR rate.