Rates of adherence to an acute pharyngitis practice guideline in the retail clinic setting were measured as an indicator of clinical quality. An analysis of 57,331 patient visits for the evaluation of acute pharyngitis was conducted. In 39,530 patients with a negative rapid strep test result, nurse practitioner and physician assistant staff adhered to guidelines in 99.05% of cases by withholding unnecessary antibiotics. Of 13,471 patients with a positive rapid strep test result, 99.75% received an appropriate antibiotic prescription. The combined guideline adherence rate for groups with positive and negative rapid strep test results was 99.15%. Strep cultures were performed on 99.1% of patients with a negative rapid strep test result, and 96.2% of patients with a positive culture were treated with an antibiotic. Finally, 0.95% of patients with a negative rapid strep test result were provided an antibiotic outside clinical guidelines; however, approximately half of these prescriptions (n = 190) were supported by documentation of clinical concerns for which an antibiotic was a reasonable choice.