INTRODUCTION: Obesity treatment is less successful for socioeconomically disadvantaged populations, particularly when delivered in primary care. Digital health strategies can extend the reach of clinical obesity treatments to care settings serving patients at highest risk. METHODS: Track was an effectiveness RCT of a 12-month digital weight-loss intervention, embedded within a community health center system. Participants were 351 adult patients (aged 21-65 years) with obesity and hypertension, diabetes, and hyperlipidemia. Patients were randomized to usual care (n=175) or an intervention (n=176) comprising app-based self-monitoring of behavior change goals with tailored feedback, a smart scale, dietitian-delivered counseling calls, and clinician counseling informed by app-generated recommendations, delivered via electronic health record. The primary outcome was 12-month weight change. Randomization began on June 18, 2013, final assessments were completed on September 10, 2015. Data analysis was conducted in 2016 and 2017. The trial retained 92% of usual care and 96% of intervention participants at 12 months. RESULTS: The Track intervention produced larger weight losses relative to usual care at 6 months (net effect: -4.4 kg, 95% CI= -5.5, -3.3, p<0.001) and 12 months (net effect: -3.8 kg, 95% CI= -5.0, -2.5, p<0.001). Intervention participants were more likely to lose ≥5% of their baseline weight at 6 months (43% vs 6%, p<0.001) and 12 months (40% vs 17%, p<0.001). Intervention participants completing ≥80% of expected self-monitoring episodes (-3.5 kg); counseling calls (-3.0 kg); or self-weighing days (-4.4 kg) lost significantly more weight than less engaged intervention participants (all p<0.01). CONCLUSIONS: A digital obesity treatment, integrated with health system resources, can produce clinically meaningful weight-loss outcomes among socioeconomically disadvantaged primary care patients with elevated cardiovascular disease risk. TRIAL REGISTRATION: This study is registered at www.clinicaltrials.gov NCT01827800.