Significant evidence has shown that radiation therapy for patients with nasopharyngeal cancer (NPC) can cause swallowing abnormality. Based on our prior cross-sectional study for 184 NPC patients from 1995 to 1999, the findings of videofluoroscopic swallowing study (VFSS) revealed continuous deterioration of swallowing function of these patients even many years after radiation. We conducted a prospective study to evaluate the longitudinal change of swallowing function based on VFSS before, one month, one year and two years after completing radiation therapy. The amount of saliva was measured at the same time of VFSS study to test the relationship of decreased amount of saliva and swallowing function. Comparison of serial VFSS studies in NPC patients (n=84) and normal volunteers (n=38) were obtained. We assume that this study may reveal a complete understanding of changing swallowing patterns in the course of radiation therapy of patients with NPC. From this study, NPC patients can understand their own swallowing function. Therefore, the information may enable for earlier intervention of swallowing training or correction to avoid morbidity of radiation therapy in this patient group.