Importance: Accurate, accessible predictions of posttreatment hearing loss for patients with head and neck cancer prior to the initiation of treatment are a necessary part of informed patient decision-making. Objective: To develop a prediction model for postradiotherapy and/or post-cisplatin chemotherapy hearing loss for patients with head and neck cancer. Design, Setting, and Participants: A retrospective cohort study was conducted at a tertiary academic medical center among 242 patients (482 ears) with head and neck cancer who were treated with radiotherapy and/or cisplatin from October 1, 2014, to July 31, 2018, and had follow-up audiometric data available. Exposures: Radiotherapy and cisplatin chemotherapy. Main Outcomes and Measures: Patient hearing level, as measured by the mean of pure tone audiometry at 1, 2, and 4 kHz on completion of treatment. A multivariable mixed model for predicting the posttreatment pure tone average was developed using only information available to clinicians at the beginning of treatment. Results: A total of 242 patients (482 ears; 56 women and 186 men; mean [SD] age, 60  years) were included in the analysis. All patients in the study received radiotherapy, and 105 (43.4%) received cisplatin chemotherapy. The mean (SD) total cumulative cisplatin dose was 298 (109) mg/m2. Patients' ears received a mean (SD) cochlear radiotherapy dose of 15 (13) Gy. The fixed-effects predictions from the predictive model agreed with 77% (95% CI, 73%-81%) of the variability in the posttreatment pure tone average. This predictive model also had a sensitivity of 80% and a specificity of 75% for predicting an observed posttreatment pure tone average greater than 35 dB (area under the receiver operating characteristic curve, 0.85). Conclusions and Relevance: To our knowledge, this study develops the first accurate prediction model of posttreatment hearing in patients with head and neck cancer that is feasible for use in the clinical setting before the initiation of treatment. This research confirms that exposure of the cochlea to cisplatin chemotherapy and radiotherapy is associated with hearing loss in patients with head and neck cancer. Finally, this research motivates future studies of ototoxic effects to better understand the adverse effects of head and neck cancer treatment..