Clinical research shows that nutritional intervention is necessary to prevent malnutrition in head and neck cancer patients undergoing radiotherapy. The objective of the present study was to assess the value of individually adjusted counselling by a dietitian compared to standard nutritional care (SC). A prospective study, conducted between 2005 and 2007, compared individual dietary counselling (IDC, optimal energy and protein requirement) to SC by an oncology nurse (standard nutritional counselling). Endpoints were weight loss, BMI and malnutrition (5 % weight loss/month) before, during and after the treatment. Thirty-eight patients were included evenly distributed over two groups. A significant decrease in weight loss was found 2 months after the treatment (P = 0·03) for IDC compared with SC. Malnutrition in patients with IDC decreased over time, while malnutrition increased in patients with SC (P = 0·02). Therefore, early and intensive individualised dietary counselling by a dietitian produces clinically relevant effects in terms of decreasing weight loss and malnutrition compared with SC in patients with head and neck cancer undergoing radiotherapy.