The aim of this prospective study was to investigate the incidence of weight loss in head and neck cancer patients on commencing radiotherapy treatment at a regional oncology centre. Of the 100 patients included in the study, 33% presented with carcinoma of the larynx. Fifty-seven per cent of patients had lost weight on commencing treatment. A mean weight loss of 6.5 kg, equating to approximate to 10% of body weight, was reported. A significant number of patients experienced a dry and/or sore mouth, had difficulty masticating and swallowing food, had altered taste perception, were missing meals or had symptoms of uncontrollable nausea and constipation. Since radiotherapy treatment may further limit oral intake, it is essential that dietetic intervention is addressed for all head and neck cancer patients and incorporated into the treatment plan on diagnosis before definitive management commences.