To measure baseline human papillomavirus (HPV) vaccination rates among tertiary and community-based Otolaryngology - Head and Neck Surgery (Oto-HNS) clinic patients and to determine risk factors for under-vaccination. Retrospective chart review of patients aged 9 to 26 years presenting to an Oto-HNS clinic from 2017 to 2019. Patients were considered complete for HPV vaccination if they received two doses of HPV vaccine with the first dose received before age 15 years or three doses of HPV vaccine otherwise. 8,532 unique patients met the criteria. At the index visit, 3,110 (36.5%) had completed the HPV series, 5,422 (63.5%) were due for one or more doses, with 4,981 (58.4%) eligible for vaccination at the time of their appointment. Of those dues, most (3,148/5,422 or 58%) were past due by age (≥13 years old). Of the 3,148 patients past due, 745 (23.7%) were partially vaccinated and 2,403 (76.3%) were vaccine naïve. Male sex and younger age were both independently associated with incomplete vaccination (p < 0.0001). This study demonstrates that the implementation of on-site HPV vaccination has the potential to increase the opportunities for vaccination among vaccine-eligible patients, especially among young males. Otolaryngologists have the potential to provide meaningful preventive services in the fight against HPV-mediated disease. 3 Laryngoscope, 133:116-123, 2023.