Patients undergoing radical radiotherapy for head and neck cancers often experience significant complications. We sought to evaluate the impact of prophylactic gastrostomy tubes (PGTs) among these patients on four easily evaluable adverse outcomes, namely, absolute weight loss, percentage weight loss, admissions for nutritional reasons and treatment interruptions. A retrospective review was carried out on patients undergoing radical radiotherapy for primary head and neck cancers from September 1999 to October 2005 at the Wellington Blood and Cancer Centre (n = 71). PGTs were placed in 7 (10%) patients. Patients with PGTs were compared with the patients without PGTs (the control group) by univariate and multivariate analyses. By univariate analysis, there was no significant difference in absolute or percentage weight loss between those with PGTs and the control group. By multivariate analysis, those with PGTs lost 5.2% (P = 0.016) less weight than the control group. There were no significant differences between the two groups with regard to admissions for nutritional reasons or treatment interruptions. The use of PGTs can reduce weight loss in patients undergoing radical radiotherapy for head and neck cancers, and its use should be further evaluated in future studies.