['The aims of the present study were to explore pre-treatment predictors of weight loss during radiation treatment only in head and neck cancer (HNSCC) patients and investigate the weight loss in patients with or without a feeding tube.', 'Retrospectively, weight change during curative radiotherapy was investigated in 476 consecutive HNSCC patients. Independent predictors were identified using multivariate regression analysis with weight loss below or above 5 % as the primary dependent variable.', 'Baseline BMI, tumor site, and stage predicted weight loss above 5 %. The odds of weight loss above 5 % in patients with BMI >25 were 3.00\u2009±\u20090.64 times higher compared with patients with BMI <25 (p\u2009<\u20090.0001). Patients with pharyngeal, oral cavity, or supraglottic tumors had 3.12\u2009±\u20090.80 times higher odds of weight loss above 5 % compared with glottic cancer patients (p\u2009<\u20090.0001), and the odds were 1.68\u2009±\u20090.40 times higher in stage III-IV patients compared with stage I-II patients (p\u2009=\u20090.03). Seperate analyses revealed that tumor site and stage only predicted weight loss in patients with BMI >25 but not in patients with BMI <25. Patients receiving a feeding tube weighed less than patients without (73.8 vs 78.3 kg) and feeding tube reduced, but did not prevent, weight loss which averaged 6.7\u2009±\u20094.7 kg (7.4\u2009±\u20094.7 %) compared with 4.7\u2009±\u20095.9 kg (5.5\u2009±\u20096.0 %) in patients without a feeding tube (P\u2009<\u20090.0001).'] Is prediction of critical weight loss during radiation treatment in head and neck cancer patients dependent on BMI?