Purpose Head and neck cancer patients have a high risk of malnutrition and swallowing dysfunction. This study reports on adherence and nutrition outcomes with the use of local evidence-based guidelines for the nutrition management of patients with head and neck cancer, including placement of proactive gastrostomy tubes for high risk patients. Methods This study is a prospective observational audit in patients treated for head and neck cancer at a tertiary hospital from 2007 to 2008 (n?=?539). Nutrition outcomes (weight, nutritional status and type of nutrition support) were compared for each nutrition risk category. Primary outcome was 10 % or more weight loss at 3 months post-treatment (n?=?219). Results Overall adherence to the guideline tube feeding recommendations was 81 %. High risk patients had mean weight loss of 6 % on completion of treatment and 9 % at 3 months post-treatment, despite the majority having a proactive gastrostomy tube. Medium and low risk patients also lost weight over this time. Univariate analysis found that non-adherence to the guidelines was associated with weight loss at 3 months (p?=?0.013). Multivariate analysis found overweight patients had 1.82 greater odds, and obese patients had 3.49 greater odds of losing weight (p?=?0.021). Patients with significant weight loss at diagnosis had decreased odds of losing weight later (p?=?0.011). Conclusion Clinically significant weight loss was still prevalent in this population despite proactive interventions. Predictors of weight loss support the evidence-based guidelines' risk categories, and adherence was important to improve outcomes. Further research is required to determine the impact of significant weight loss in patients with high body mass index (BMI).