ABSTRACT: For locally advanced head and neck squamous cell carcinoma (HNSCC), therapeutic decisions depend on comorbidity or age. We estimated the treatment outcomes of patients with different Charlson comorbidity index (CCI) scores and ages to determine whether aggressive treatment improves survival.Data from the Taiwan National Health Insurance and cancer registry databases were analyzed, and we included >20-year-old patients with American Joint Committee on Cancer (AJCC) stage III or IV HNSCC (International Classification of Diseases, Ninth Revision, Clinical Modification codes 140.0-148.9) undergoing surgery, chemotherapy (CT), radiotherapy (RT), concurrent chemoradiotherapy (CCRT), sequential CT and RT, or surgery with adjuvant treatment. The exclusion criteria were a past cancer history, distant metastasis, AJCC stage I or II, missing sex data, an age < 20 years, nasopharyngeal cancer, in situ carcinoma, sarcoma, and HNSCC recurrence. The index date was the date of first HNSCC diagnosis, and comorbidities were scored using the CCI. The enrolled patients were categorized into Group 1 (curative-intent aggressive treatments) and Group 2 (best supportive care or palliative treatments).We enrolled 21,174 stage III or IV HNSCC patients without distant metastasis (median follow-up, 3.25 years). Groups 1 and 2 comprised 18,584 and 2232 patients, respectively. After adjustment for age, sex, and clinical stage, adjusted hazard ratios (95% confidence intervals) of overall death in Group 1 were 0.33 (0.31-0.35), 0.34 (0.31-0.36), and 0.37 (0.28-0.49), and those of all-cause death among patients undergoing curative surgical aggressive treatments were 1.13 (0.82-1.55), 0.67 (0.62-0.73), and 0.49 (0.46-0.53) for CCI scores of ?10, 5 to 9, and <5, respectively.Aggressive treatments improve survival in elderly (?65 years) and critically ill HNSCC patients. Curative nonsurgical aggressive treatments including definitive RT or CCRT might be suitable for HNSCC patients with CCI scores ?10.