Nutritional support is becoming a mainstay of the comprehensive therapeutic approach to patients with chronic diseases. Chronic heart failure (CHF) and chronic obstructive pulmonary disease (COPD) are frequently associated with the progressive development of malnutrition, due to reduced energy intake, increased energy expenditure and impaired anabolism. Malnutrition and eventually cachexia have been shown to have a negative influence on the clinical course of CHF and COPD, and to impinge on patients' quality of life. Nutritional support in these patients should be therefore considered, particularly to prevent progressive weight loss, since restoration of lean and fat body mass may not be achievable. In CHF and COPD patients, the gastrointestinal tract is normally accessible and functioning. Although recent reports suggest that heart failure is associated with modifications of intestinal morphology, permeability and absorption, the clinical relevance of these are still not clear. Oral supplementation and enteral nutrition should represent the first choices when cardiopulmonary patients need nutritional support, particularly given the potential complications and economic burden of parenteral nutrition. This appropriately preferential enteral approach partly explains the lack of robust clinical trials of the role of parenteral nutrition in CHF and COPD patients. Based on the available evidence collected via PubMed, Medline, and SCOPUS searches, it is recommended that parenteral nutrition is reserved for those patients in whom malabsorption has been documented and in those in whom enteral nutrition has failed.