Diet is important for both quality of life (QoL) and survival of patients with oral cancer. Their intake of food is impeded by functional restrictions in chewing and swallowing. In the DÖSAK REHAB STUDY 1652 patients from 38 hospitals within the German-language area of Germany; Austria and Switzerland were examined with regard to functional and psychological variables having an impact on diet. Chewing and swallowing are correlated with mobility of the tongue and the mandible as well as opening of the mouth. Thirty five percent of the patients lost weight; 41% maintained their weight and 24% gained weight. The QoL of patients who were able to maintain their weight and of those who gained weight was significantly better than that of patients who lost weight. A normal diet was important for maintaining weight. Mashed food; liquid food and loss of appetite were closely associated with loss of weight; although it was possible for nutritional counseling and dietary support to be implemented particularly favorably in this respect. Due to problems with eating patients' strength deteriorated; thus restricting activity. Radiotherapy had a negative impact on diet and weight. It influenced sense of taste; dryness of the mouth; swelling and discomfort when ingesting food. Pain and scars in the region of the operation also cause patients to dislike hard; spicy and sour food. Support from a nutritional counselor in implementing a calorie-rich diet remedied this and such support needs to be integrated into patient management. The fact that a poor nutritional status is of such great importance is well-known; but what is often lacking is the systematic implementation of continued professional nutritional counseling over a long period of time; weight control and psycho-social support of the operated patients; particularly those who also have had radiotherapy.