OBJECTIVES: Nurse practitioners (NPs) and physician assistants (PAs) have increasingly broad prescribing authority in the United States, yet little is known regarding whether they deliver the same quality of pharmacologic care as physicians. We sought to compare the quality of ambulatory pharmacologic care provided by NPs, PAs and physicians. METHODS:  We used a serial cross-sectional analysis of 2006-2012 National Ambulatory Medical Care Survey (NAMCS) and National Hospital Ambulatory Medical Care Survey (NHAMCS) to examine ambulatory care services in physician offices, hospital emergency departments and outpatient departments. Participants included a nationally representative sample of patient visits to physicians, NPs and PAs and main outcome measures included thirteen validated outpatient quality indicators focused on pharmacological management of chronic diseases and appropriate medication use. RESULTS:  A total of 701,499 sampled patient visits were included during the study period, which represented an estimated 8.33 billion visits nationwide. Physicians were the primary provider for 96.8% of all outpatient visits examined, while NPs and PAs each accounted for 1.6% of these visits. The proportion of eligible visits where quality standards were met ranged from 34.1% (angiotensin converting enzyme [ACE]-inhibitor use for congestive heart failure) to 89.5% (avoidance of inappropriate medications among elderly). The median overall performance across all indicators was 58.7%. On unadjusted analyses, there were statistically significant differences in quality of care between non-physicians and physicians for each indicator. After adjustment for potentially confounding patient and provider characteristics, the quality of pharmacologic care delivered by non-physician providers was similar to the care delivered by physicians for ten of the thirteen indicators evaluated, and there was no consistent directional association between provider type and indicator fulfillment for the remaining measures. CONCLUSIONS:  While there were significant shortfalls in the quality of ambulatory pharmacologic care among these visits, the quality of care delivered by non-physicians and physicians was generally comparable.