The clinical importance of tumor-induced cachexia is indicated by the fact that two thirds of the cancer patients suffer from it and it plays an outstanding role in mortality of the disease. The onset of the tumorous anorexia/cachexia syndrome does not depend on tumor burden or the stage of the disease. The syndrome is very complex in nature and cannot be reversed by "over-feeding" of the patient. The appropriate supply of calories, carbohydrates, proteins and lipids is impossible, therefore administration of nutrients which do not cause volume-load for the patient is justified. Enteral feeding must be the primary aim in cancer patients till the gastrointestinal tract is functioning. To improve appetite and increase body weight specific pharmacological intervention may also be necessary. Understanding the molecular mechanisms of the development of tumorous anorexia/cachexia syndrome opens new ways of treatment.