Background: The objectives of this study were to investigate the incidence of high-risk genotypes of human papillomavirus (HPV) in tumours of patients with oropharyngeal squamous cell carcinoma (OPSCC) during an 18-year period in Eastern Denmark. Methods: In this population-based, consecutive, semi-national registry study, all patients diagnosed with OPSCC from 2000 to 2017 in Eastern Denmark were evaluated at head and neck oncological departments at public university hospitals. Analyses included tumour characteristics (HPV-positive [HPV+] versus HPV-negative [HPV–]), age-adjusted incidence rates (AAIRs), average annual percentage change (AAPC) of OPSCC, and patient demographics. All HPV+ cases from 2011 to 2017 were genotyped. Results: In total, 55% of 2169 OPSCC cases were HPV+. HPV16, HPV33, HPV35 or other types were found in 86%, 7.4%, 3.4% and 3.2% of cases, respectively. The AAIR per 100,000 of all OPSCCs was 1.8 in 2000, which increased to 5.1 in 2017 (HPV+: threefold increase, HPV–: twofold increase). The AAPC from 2000 to 2017 increased by 7% (HPV+ increased by 10% and HPV– by 4%). The median age at diagnosis for all OPSCC cases increased during the 18-year study period (HPV+: 58–61 years, p < 0.001; HPV–: 60–65 years, p < 0.001). Conclusion: We report a threefold increase in OPSCC incidence during the 18-year observation period and a significant increase in median age at diagnosis. Over 93% of HPV genotypes in HPV+ OPSCC are included in current HPV vaccines except for HPV35 (4%). HPV vaccination of both sexes is advised to halt this emerging cancer epidemic.