Background: Ukraine's HIV epidemic is concentrated among people who inject drugs (PWID), however, coverage with opioid agonist therapies (OATS) available mostly at specialty addiction clinics is extremely low. OAT integrated into primary healthcare clinics (PHCs) provides an opportunity for integrating comprehensive healthcare services and scaling up OAT. Methods: A pilot study of PHC-based integrated care for drug users conducted in two Ukrainian cities between 2014 and 2016 included three sub-studies: 1) cross-sectional treatment site preference assessment among current OAT patients (N=755); 2) observational cohort of 107 PWID who continued the standard of care versus transition of stabilized and newly enrolled PWID into PHC-based integrated care; and 3) pre/post analysis of attitudes toward PWID and HIV patients by PHC staff (N=26). Results: Among 755 OAT patients, 53.5% preferred receiving OAT at PHCs, which was independently correlated with convenience, trust in physician, and treatment with methadone (vs. buprenorphine). In 107 PWID observed over 6 months, retention in treatment was high: 89% in PWID continuing OAT in specialty addiction treatment settings (standard of care) vs 94% in PWID transitioning to PHCs; and 80% among PWID newly initiating OAT in PHCs. Overall, satisfaction with treatment, subjective self-perception of well-being, and trust in physician significantly increased in patients prescribed OAT in PHCs. Among PHC staff, attitudes towards PWID and HIV patients significantly improved over time. Conclusions: OAT can be successfully integrated into primary care in low and middle-income countries and improves outcomes in both patients and clinicians while potentially scaling-up OAT for PWID. (C) 2017 Elsevier B.V. All rights reserved.