Background: Recent evidence has suggested links between obesity and outcomes for various types of cancer. This study investigates the impact that body composition has on survival in patients with head and neck cancer. Methods: Data prospectively collected from 578 patients were analyzed using Cox regression models to determine independent associations that pretreatment body mass index (BMI) and 3-month weight change have on observed survival. Results: Higher BMIs were associated with better survival (p<.001). Five-year rates ranged from 33.8% for underweight to 75.3% for overweight/obese patients. Patients with stable weight had the highest 5-year rate (72.6%; p=.019), while patients who gained ≥5% had worse survival (45.8%) than those who lost ≥5% (65.8%). BMI independently predicted survival, while weight change was not an independent predictor. Conclusions: This demonstrated association between BMI and survival provides useful information when offering prognoses and investigating optimal treatments. This article is protected by copyright. All rights reserved.