Malnutrition occurs in 23-70% of patients with chronic obstructive pulmonary disease and appears to be an independent factor connected with poor prognosis. Malnutrition stems from a long-term negative balance of energy and nutrients. That is caused by hypermetabolism, with possible role of an increased thermic effect of food, and probably by (at least intermittently) a limited intake of food. The adverse effect of malnutrition may be mediated by a decreased respiratory muscle strength but also by other mechanisms (electrolyte disorders, disturbed respiratory control, immunosuppression). In these patients, realimentation may be difficult to achieve, especially on the out-patient basis. However, with an increased effort of the health professionals and a good compliance of the patients, a substantial improvement is feasible, which might in turn improve the patients' prognosis.