To examine changes in health-related quality of life among oropharyngeal cancer patients by stages and across treatment types among advanced cancer patients. Individual prospective cohort study. All newly diagnosed patients with oropharyngeal cancer treated with curative intent were routinely assessed. The European Organization for Research and Treatment of Cancer (EORTC) both the Main Module quality-of-life questionnaire (QLQ-C30) and the Head and Neck Cancer (HNC) Module (QLQ-H&N35) were administered at diagnosis and 3, 6, and 12 months thereafter. Complete case analysis was used following assessment of missing data. The proportion of patients with clinically significant deterioration (changes of ≥ 10 points) from baseline were calculated for each follow-up time point and compared by stage (I/II vs. III/IV) and then treatment type (chemotherapy and radiotherapy [CRT] vs. surgery and postoperative radiotherapy [S&PORT]). Deterioration in most domains was most frequent for stage III/IV patients at 3 months (both modules), whereas stage I/II patients experienced this at 6 months (QLQ-C30) and 12 months (H&N35). Among stage III/IV patients, this happened at all time points for S&PORT patients (QLQ-C30) versus 12 months for CRT patients (H&N35). The number of patients reporting deterioration was lower for most domains at 12 months compared to earlier periods, although dry mouth remained a problem for most patients (60%-85% across treatment/stage groups). Our preliminary findings suggest that general and disease-specific deterioration is of most concern for stage I/II patients at 6 and 12 months and at 3 months for advanced cancer patients. For stage III/IV patients receiving S&PORT, general deterioration remains a problem after diagnosis, whereas for CRT patients, disease-specific deterioration is of most concern at 12 months.