The pathogenesis of cancer anorexia/cachexia is still unclear, partly explaining why its treatment remains disappointing. Anorexia plays a central role but cancer cachexia is more complex than chronic starvation. One of the key differences is the preferential mobilization of fat and the sparing of skeletal muscle in simple starvation compared to an equal mobilization of fat and skeletal muscle in cancer patients. An increase in basal energy expenditure also appears to play a contributory role in many patients. Cytokines, essentially but not exclusively tumor necrosis factor-α, play an essential pathogenic role and the syndrome can be compared to a low grade chronic inflammatory state.Parenteral nutrition could facilitate the administration of complete doses of chemotherapy or radiotherapy but no significant survival benefit or decrease in treatment-induced toxicity have been demonstrated in prospective randomized trials. The gut should have the preference for nutritional support. Percutaneous endoscopic gastrostomy is used more and more often in patients with a functionally intact gastroinestinal tract, especially in patients with head and neck cancer. Progestational drugs can to some extent stimulate appetite, food intake, energy level, increase weight and decrease the severity of nausea and vomiting. However, pharmacological treatment of cancer cachexia remains disappointing and more trials with anticytokine drugs, anabolic agents or polyunsaturated fatty acids should be conducted.