It is well recognised that radical chemoradiotherapy (CRT) for head and neck cancers can significantly affect swallowing, especially if radiotherapy is delivered to the hypopharynx and/or both sides of the neck. As such, prophylactic gastrostomy tubes are often advocated in advance of CRT to these sites, in order to ensure optimal nutrition during treatment and avoid admissions for nasogastric tube placement and feeding. The counterargument to prophylactic gastrostomy tube placement relates to concerns that placing such tubes results in less motivation for patients to continue swallowing during treatment, leading to worse long-term swallowing outcomes. This prospective observational cohort study recruited 116 patients who underwent prophylactic percutaneous endoscopic gastrostomy (PEG) placement prior to receiving radical CRT for advanced head and neck malignancies. The majority of patients (52; 44.8%) were treated for cancers of the nasopharynx followed by the oropharynx (27; 23.3%), larynx and oral cavity (13 each site; 11.2%) and hypopharynx (11; 9.5%). The majority of patients (110; 94.8%) used their PEGs, 70 fully and 40 partially. Non-users lost more weight than partial or full users, although this difference did not achieve statistical significance (p = 0.085). Full users of PEGs had a significantly longer time of tube dependence than partial users (7.0 months versus 4.9 months, p = 0.012). The overall PEG-dependence rate at 12 months was 5.5%; 12.9% of full users were tube dependent at 12 months versus 5.0% of partial users, although this difference was not significant (p = 0.186). Complications of PEG placement were minimal with the principal reported issue relating to infection (14.7% of patients affected). The data from this paper would tend to support the use of prophylactic gastrostomies for patients receiving CRT for advanced head and neck malignancies. The longer time of tube dependence and trend towards a higher rate of long-term tube dependence associated with full tube use would also support continued strong encouragement of patients to maintain oral intake as far as possible during treatment, with only partial use of their gastrostomy tubes if at all feasible.