OBJECTIVES:  To identify clinical, demographic and healthcare delivery correlates of 12 week treatment adherence among patients initiating direct acting antivirals (DAAs) including sofosbuvir-based (with ribavirin or ribavirin+peginterferon or semeprivir), ledipasvir/sofosbuvir –based and ombitasvir/paritaprevir/ritonavir-dasabuvir –based regimens. METHODS: Patients of a regional health plan in Western Massachusetts with ≥1 prescription claim for a DAA agent between January 1, 2014 and April 1, 2016, eligible for coverage 6 months before and after DAA initiation were included. The primary outcome was 90 day adherence defined as proportion of days covered (PDC) ≥ 90%. Independent variables included baseline comorbidities (HIV, opioid dependence, mental and general health comorbidities), DAA treatment modality (three broad regimens described above), type of insurance coverage (commercial vs Medicaid (MassHealth)), initial prescription cost-sharing, prescriber specialty (gastroenterology/hepatology vs other) and type of dispensing pharmacy (mail-order specialty vs hospital specialty pharmacy). The covariates included age, gender and year of therapy initiation. RESULTS:  In total, 138 patients were included in the analyses. Overall, 70.3 % of patients had PDC of ≥90% with mean (SD) PDC of 73.7% (18.7). The multivariate logistic regression analysis showed that presence of HIV diagnosis ([OR] = 0.14; 95% CI, 0.02-0.91) and type of insurance coverage ([OR] = 7.51; 95% CI, 1.98-28.47) were significantly associated with 90-day DAA adherence. Patients with HIV and those covered by MassHealth were significantly less likely to fill 12 weeks of DAA-based therapy. Type of dispensing specialty pharmacy, prescriber specialty, opioid dependence and cost-sharing were not associated with 90-day adherence in this study (p>0.05). CONCLUSIONS: With significant expansion of access to DAA therapy among Medicaid patients in Massachusetts in August 2016, additional adherence support is needed to ensure patients complete the course of treatment and achieve treatment response. Prescribers may also consider providing adherence support to patients with comorbid HIV diagnosis to ensure DAA treatment completion.