Importance: Head and neck cancer (HNC) and its treatment may negatively alter neurocognitive and speech functioning. However, the prevalence of neurocognitive impairment among patients with HNC before treatment is poorly studied, and the association between neurocognitive and speech functioning is unknown, which hampers good interpretability of the effect of HNC treatment on neurocognitive and speech function. Objectives: To document neurocognitive functioning in patients with HNC before treatment and to investigate the association between neurocognitive and speech functioning. Design, Setting, and Participants: Prospective cohort study of newly diagnosed patients with HNC before treatment using a large sample obtained in a nationwide, multicenter setting (Netherlands Quality of Life and Biomedical Cohort Study in Head and Neck Cancer [NET-QUBIC] project). Main Outcome and Measures: Objective neuropsychological measures of delayed recall, letter fluency, and executive functioning, as well as patient-reported outcome measures on neurocognitive speech and functioning, were collected before treatment. Results: In total, 254 patients with HNC participated (71.7% male), with a mean (SD) age of 62 (10) years. The response rate ranged from 81.9% (208 of 254) to 84.6% (215 of 254). Objective neurocognitive measures indicated that 4.7% (10 of 212) to 15.0% (32 of 214) of patients were initially seen with moderate to severe cognitive impairment. Mild to moderate impairment was found in 12.3% (26 of 212) to 26.2% (56 of 214) of patients. The most altered domains were delayed recall and letter fluency. Seven percent (15 of 208) of the patients reported high levels of everyday neurocognitive failure, and 42.6% (89 of 209) reported speech problems. Objective neurocognitive function was not significantly associated with patient-reported neurocognitive or speech functioning, but the results from patient-reported outcome measures were significantly correlated. Conclusions and Relevance: Results of this study demonstrate a high prevalence of impaired speech functioning among patients with HNC before treatment, which is in line with previous findings. A novel finding is that neurocognitive impairment is also highly prevalent as objectively measured and as self-perceived. Understanding the reason why patients with HNC are initially seen with neurocognitive impairment before the start of treatment is important because this impairment may complicate patient-clinician interaction and alter treatment adherence and because treatment itself may further worsen cognitive functioning. In addition, low self-perceived neurocognitive and speech functioning before treatment may decrease a patient's confidence in communicative participation and perceived quality of life. Disentangling the associations between objective and patient-reported neurocognitive and speech functions is an important area for future research.