Background: Due to differential training, nurse practitioners (NPs) and physicians may provide different quantities of services to patients. Purpose: To assess differences in the number of laboratory, imagining, and procedural services provided by primary care NPs and physicians. Methods: Secondary analysis of 2012-2016 National Ambulatory Medical Care Survey (NAMCS), containing 308 NP-only and 73,099 physician-only patient visits, using multivariable regression and propensity score techniques. Findings: On average, primary care visits with NPs versus physicians were associated with 0.521 fewer laboratory (95% CI -0.849, -0.192), and 0.078 fewer imaging services (95% CI -0.103,-0.052). Visits for routine and preventive care with NPs versus physicians were associated with 1.345 fewer laboratory (95% CI -2.037,-0.654), and 0.086 fewer imaging services (95% CI -0.118,-0.054) on average. Primary care visits for new problems with NPs versus physicians were associated with 0.051 fewer imaging services (95% CI -0.094,-0.007) on average. Discussion: NPs provide fewer laboratory and imaging services than physicians during primary care visits. Cite this article: Patel, E., Kandrack, R., (2021, September/October). Differences in the number of services provided by nurse practitioners and physicians during primary care visits. Nurs Outlook, 69(5), 886-891. https://doi.org/10.1016/j.outlook.2021.04.003.