Background:/Aims: Immunization is the most effective clinical preventive service for children. While a large body of literature exists on racial disparities in health, data on immunization disparities is limited and the results are varied. Goals of this study were to evaluate whether racial/ethnic disparities in immunization completion rates by age 2 years remain after adjusting for other factors, And to explore potential system-level factors that may be contributing to the disparity. Methods: This was a retrospective cohort study which included clinic patients who had their second birthday between January 1, 2009 and December 31, 2013, and who had at least one primary care visit to a clinic within the 6 months before their second birthday. A full cohort and a mother matched nested cohort with more granular race data and additional factors were both analyzed. Vaccines were identified using the electronic health record. The primary outcome was completion of the infant immunization schedule by 2 years of age. Logistic regression was used to evaluate associations. Results: The full cohort included 23,601 subjects of which 10,125 (43%) were non-White. At age 24 months the non-White patients had a completion rate of 75% and the White patients had a completion rate of 79%. After adjustment, non-White patients were less likely to be vaccinated (OR: 0.89, 95%CI: .83-.94). Rates were significantly improved by more clinic visits, well child visits and white race. The nested mother matched cohort included 9,066 subjects of which 3,324 (37%) were non-White. The completion rates varied from 76.9% for East African origin to 83.3% for White. After adjustment of other factors, only in the East African origin group (primarily Somali) was the rate significantly lower than the White group (0.53, 0.4-0.70). Other characteristics that were associated with improved completion were greater number of visits, having a well-child visit and more total months with insurance. Conclusion: We observed modest disparities in vaccine series completion by age 2. These results suggest two strategies for decreasing the disparity in completion: outreach to schedule well child visits and structural changes in insurance to make continuous coverage more likely.