IMPORTANCE Prospective studies are needed to examine the temporal relationship between oral human papillomavirus (HPV) detection and risk of head and neck squamous cell carcinoma (HNSCC). Moreover, the oral cavity contains a wide spectrum of alpha-, beta-, and gamma-HPV types, but their association with risk of HNSCC is unknown. OBJECTIVE To prospectively examine associations between beta-, beta-, and gamma-HPV detection in the oral cavity and incident HNSCC. DESIGN A nested case-control study was carried out among 96 650 participants, cancer free at baseline, with available mouthwash samples in 2 prospective cohort studies: (1) the American Cancer Society Cancer Prevention Study II Nutrition Cohort and (2) the Prostate, Lung, Colorectal, and Ovarian Cancer Screening Trial. Incident cases of HNSCC (n = 132) were identified during an average 3.9 years of follow-up in both cohorts. Three controls per case (n = 396) were selected through incidence density sampling and matched on age, sex, race/ethnicity, and time since mouthwash collection. METHODS Through a next-generation sequencing assay, DNA from alpha-, beta-, and gamma-HPV types were detected. Conditional logistic regression models were used to estimate odds ratios (ORs) and 95% CIs, adjusting for smoking history, alcohol consumption, and detection of HPV-16 for beta-and gamma-HPVs. MAIN OUTCOMES AND MEASURES Incident HNSCC, which includes cancers of the oropharynx, oral cavity, and larynx. RESULTS A total of 132 participants developed HNSCC during the follow-up period (103 men and 29 women; average age at baseline, 66.5 years). Oral HPV-16 detection was associated with incident HNSCC (OR, 7.1; 95% CI, 2.2-22.6), with positive association for oropharyngeal SCC (OR, 22.4; 95% CI, 1.8-276.7), but not for oral cavity (OR, 4.5; 95% CI, 0.6-34.7) or laryngeal SCCs (OR, 0.11; 95% CI, 0.01-834.80). Detection of beta 1-HPV-5 and beta 2-HPV-38 types, as well as gamma-11 and gamma-12 species, had ORs for HNSCC that ranged from 2.64 to 5.45 (P < .01 for all comparisons). Detection of beta 1-HPV-5 type was associated with oropharyngeal (OR, 7.42; 95% CI, 0.98-56.82; P = .054), oral cavity (OR, 5.34; 95% CI, 1.51-18.80; P = .01), and laryngeal SCCs (OR, 2.71; 95% CI, 1.00-7.43; P = .05), whereas gamma 11-and gamma 12-HPV species were associated with both oral cavity (OR, 7.47; 95% CI, 1.21-46.17; P =.03; and OR, 6.71; 95% CI, 1.47-30.75; P = .01, respectively) and laryngeal SCCs (OR, 7.49; 95% CI, 1.10-51.04; P = .04 and OR, 5.31; 95% CI, 1.13-24.95; P =.03, respectively). CONCLUSIONS AND RELEVANCE This study demonstrates that HPV-16 detection precedes the incidence of oropharyngeal SCC. Associations of other HPVs, including gamma 11-and gamma 12-HPV species and beta 1-HPV-5 type suggest a broader role for HPVs in HNSCC etiology.