ImportanceDiagnostic delay can negatively affect patient outcomes in head and neck cancer (HNC). Neck mass and other symptoms of undiagnosed HNC may be treated with antibiotics, delaying diagnosis and treatment, despite current clinical practice guidelines.ObjectiveTo investigate temporal trends, associated factors, and time from symptom onset to antibiotic prescribing before an HNC diagnosis.Design, Setting, and ParticipantsA retrospective cohort study was conducted using data obtained from a deidentified electronic health records data set from January 1, 2011, to December 31, 2018. Patients with HNC enrolled in the data set for at least 1 year before diagnosis date determined by either 1 inpatient encounter or first of 2 outpatient encounters within 6 months were included. Data analysis was conducted from May 1 to November 9, 2022.ExposureAntibiotic prescription within 3 months before HNC diagnosis date.Main Outcomes and MeasuresThe primary outcome was days from the first documented symptom to HNC diagnosis.ResultsThe cohort included 7811 patients with HNC (4151 [53.1%] men, mean [SD] age, 60.2 [15.8] years). At least 1 antibiotic was prescribed for 1219 patients (15.6%) within 3 months before HNC diagnosis. This represented an increase over the 8.9% prescribing rate during the baseline period 12 to 9 months before diagnosis. The rate of antibiotic prescribing within 3 months before diagnosis did not change significantly over time (quarterly percent change, 0.49%; 95% CI, −3.06% to 4.16%). Patients receiving an antibiotic prescription within 3 months of an HNC diagnosis had a 21.1% longer time between symptom onset and HNC diagnoses (adjusted rate ratio [ARR], 1.21; 95% CI, 1.14-1.29). Compared with diagnosis by otolaryngologists, primary care/internal medicine physicians were most likely to prescribe antibiotics for patients who were diagnosed with a presenting symptom (adjusted prevalence ratio, 1.60; 95% CI, 1.27-2.02). In patients presenting with neck mass/swelling, those presenting with other symptoms were more likely to have longer intervals from symptom onset to diagnosis (ARR, 1.31; 95% CI, 1.08-1.59).Conclusions and RelevanceThe findings of this cohort study suggest there is an increased rate of antibiotic prescription in the 3 months before HNC diagnosis, which is associated with an increased time to diagnosis. These findings identify an area for improvement in HNC care and guidelines.