Background <p>Oral and swallowing dysfunction is a common complication among patients with head and neck cancer (HNC) after radiotherapy (RT) or chemoradiotherapy (CRT). However, the longitudinal course of oral and swallowing functions, particularly in patients with hypopharyngeal cancer (HPC), remains insufficiently characterized. This study aimed to comprehensively assess longitudinal changes in oral and swallowing functions in patients with HPC undergoing RT or CRT.</p> Methods <p>Twenty-seven patients with HPC were assessed before treatment (Pre) and at 1, 3, 6, and 12&#xa0;months after RT or CRT. Evaluations included respiration, neck mobility, tongue function, facial function, oral function, vocalization, swallowing function using the repetitive saliva swallowing test (RSST) and modified water swallowing test (MWST), and sensory function.</p> Results <p>Oral function worsened over time, with the increased prevalence of dry mouth and taste disturbance, whereas objective oral moisture remained relatively stable. Tongue pressure increased, while oral motor coordination declined, indicating a dissociation between strength and coordination. Swallowing efficiency decreased as reflected by RSST, while swallowing safety assessed by MWST remained stable.</p> Conclusion <p>RT/CRT induced domain-specific changes in oral function, characterized by deterioration in subjective oral symptoms and motor coordination alongside compensatory increases in tongue strength. These oral changes were associated with reduced swallowing efficiency despite preserved safety, highlighting the importance of oral-focused assessment in post-treatment management.</p>