OBJECTIVES: This study sought to evaluate the impact of the PCMH practice transformation on healthcare utilization in a Managed Medicaid population with a Hispanic majority and served specifically by safety-net clinics. METHODS: The PCMH group included eleven safety-net clinics (23,662 members) that were recognized as patient centered medical homes in late 2011 in the greater Los Angeles area, and the non-PCMH group consisted of 176 other safety-net clinics (138,152 members) in the same area . The study timeline ranged from January 2011 to December 2013 which required accounting for a concurrent federal waiver, effective June 1, 2011, under which California began transitioning senior and people with disabilities (SPDs) with fee-for-service (FFS) Medicaid into managed care systems. To avoid the potential confounding effect from the sudden influx of SPDs, the study cohort was further divided into clinic types, one with less than 10% SPD membership and the other with greater than 10%. RESULTS: Our findings show that in clinics less impacted by the SPD transition, PCMH could reduce ED visits by an average 70 visits per thousand members per year (PTMPY), avoidable ED visits by 20 visits PTMPY, and increase office visits by 1000 visits PTMPY. No significant improvements were found in clinics with SPD membership greater than 10%. CONCLUSIONS: This study further supports the effectiveness of the PCMH model in a previously untested population, while also revealing the potential limitations of the model in response to a sudden influx of heavy utilizers.