['Patients undergoing chemoradiation for head and neck squamous cell carcinoma (HNSCC) are predisposed to unplanned hospitalizations.', 'To assess the factors associated with prolonged hospitalization and its impact on patient outcomes.', 'We assessed the outcomes of patients hospitalized for ≥5 days or <5 days in 251 patients with advanced HNSCC who were undergoing radiotherapy during 2000-2012.', 'Patients who had been hospitalized for ≥5 days were more likely to be admitted for infection, acute renal failure, and/or dehydration. We found no other patient, tumor, or treatment characteristics associated with prolonged hospitalizations. Hospitalizations of ≥5 days were associated with a higher incidence of delays in radiotherapy (RT; odds ratio [OR], 2.49; 95% confidence index [CI], 1.09-5.69; 𝑃 = .03) and worse performance status after RT (OR, 5.76; 95% CI, 1.85-18.38; 𝑃 = .003). On multivariate analysis, hospitalization of ≥5 days predicted for worse local-regional control (hazard ratio [HR], 1.85; 95% CI, 1.08-3.17; 𝑃 = .03) and time to treatment failure (HR, 1.64; 95% CI, 1.03-2.61; 𝑃 = .04), and performance status after RT predicted for worse local-regional control, time to treatment failure, progression-free survival, and overall survival.'] Do hospitalizations of more than 5 days predict for worse outcomes after radiotherapy for head and neck cancer?