Background/Aims: Much of the work in antidepressant adherence relies on self-report and small sample sizes with limited racial/ethnic representation. Our study aimed to determine factors associated with poor early adherence to antidepressants in a large diverse sample of patients using pharmacy refill data. Methods: Electronic medical record data for patients 18 and older with depression who filled a new outpatient antidepressant prescription between Jan. 1, 2010, and Dec. 31, 2012, in one of six Mental Health Research Network health care systems were obtained. Self-reported race/ethnicity and pharmacy fill data were obtained from electronic medical records. Patients were considered to have early adherence if they had a second antidepressant fill within 180 days of the first. Results: 177,469 adult patients had 184,967 new episodes of depression associated with a filled antidepressant prescription. Patients refilled their antidepressants within 180 days of the first dispensing in 71% of treatment episodes. Race/ethnicity was a strong predictor of early adherence, with patients who self-identified as Asian, non-Hispanic black, Hispanic or Native Hawaiian/Pacific Islander significantly less likely to refill their antidepressant prescriptions than were non-Hispanic whites or Native Americans/Alaskan Natives. Other apparent predictors of early adherence, including neighborhood income and education, gender and prior mental health hospitalizations, were no longer significant after adjusting for race/ethnicity. Conclusion: Race/ethnicity was a robust predictor of antidepressant adherence, with racial/ethnic minority groups other than Native Americans/Alaskan Natives less likely to be adherent. Patients from these racial and ethnic minority groups may have the greatest potential benefit from targeted interventions to improve early antidepressant adherence.