Many factors can modify nutritional status in cancer patients, including cachexia, nausea and vomiting, decreased caloric intake or oncologic treatments causing malabsorption. The cachexia-anorexia syndrome is a complex metabolic syndrome associated with cancer and some other palliative conditions characterized by involuntary weight loss involving fat and muscle, anorexia, early satiety, fatigue and weakness due to shifts in metabolism caused by tumour by-products and cytokines. Cachexia is a distressing and debilitating condition, affecting significant numbers of patients with advanced disease and is the primary cause of death in about 20% of all patients with cancer. Though cachexia is most commonly associated with particular tumours, such as head and neck, gastrointestinal tract, pancreas, central nervous system and lung, it may affect any patient with any tumour at any site; no patient and no tumour are excluded. Current treatment for principally depends on its prevention rather than reversing the present disease state, and the clinical results are far from being satisfactory. A careful decision based on good clinical judgement is necessary before deciding to start either enteral or parenteral nutrition, to avoid a useless, costly and difficult treatment. Treatment should be directed toward improvement in the quality of life of the patient and should often include nutritional counseling. It should take into consideration both disease and treatment related factors as well as the cachexia syndrome itself.