Medication adherence is essential to diabetes care. Patient-physician language barriers may affect medication adherence among Latino individuals. To determine the association of patient race/ethnicity, preferred language, and physician language concordance with patient adherence to newly prescribed diabetes medications. This observational study was conducted from January 1, 2006, to December 31, 2012, at a large integrated health care delivery system with professional interpreter services. Insured patients with type 2 diabetes, including English-speaking white, English-speaking Latino, or limited English proficiency (LEP) Latino patients with newly prescribed diabetes medication. Patient race/ethnicity, preferred language, and physician self-reported Spanish-language fluency. Primary nonadherence (never dispensed), early-stage nonpersistence (dispensed only once), late-stage nonpersistence (received ≥2 dispensings, but discontinued within 24 months), and inadequate overall medication adherence (>20% time without sufficient medication supply during 24 months after initial prescription). Participants included 21 878 white patients, 5755 English-speaking Latino patients, and 3205 LEP Latino patients with a total of 46 131 prescriptions for new diabetes medications. Among LEP Latino patients, 50.2% (n = 1610) had a primary care physician reporting high Spanish fluency. For oral medications, early adherence varied substantially: 1032 LEP Latino patients (32.2%), 1565 English-speaking Latino patients (27.2%), and 4004 white patients (18.3%) were either primary nonadherent or early nonpersistent. Inadequate overall adherence was observed in 1929 LEP Latino patients (60.2%), 2975 English-speaking Latino patients (51.7%), and 8204 white patients (37.5%). For insulin, early-stage nonpersistence was 42.8% among LEP Latino patients (n = 1372), 34.4% among English-speaking Latino patients (n = 1980), and 28.5% among white patients (n = 6235). After adjustment for patient and physician characteristics, LEP Latino patients were more likely to be nonadherent to oral medications and insulin than English-speaking Latino patients (relative risks from 1.11 [95% CI, 1.06-1.15] to 1.17 [95% CI, 1.02-1.34]; P < .05) or white patients (relative risks from 1.36 [95% CI, 1.31-1.41] to 1.49 [95% CI, 1.32-1.69]; P < .05). English-speaking Latino patients were more likely to be nonadherent compared with white patients (relative risks from 1.23 [95% CI, 1.19-1.27] to 1.30 [95% CI, 1.23-1.39]; P < .05). Patient-physician language concordance was not associated with rates of nonadherence among LEP Latinos (relative risks from 0.92 [95% CI, 0.71-1.19] to 1.04 [95% CI, 0.97-1.1]; P > .28). Nonadherence to newly prescribed diabetes medications is substantially greater among Latino than white patients, even among English-speaking Latino patients. Limited English proficiency Latino patients are more likely to be nonadherent than English-speaking Latino patients independent of the Spanish-language fluency of their physicians. Interventions beyond access to interpreters or patient-physician language concordance will be required to improve medication adherence among Latino patients with diabetes.