Changes in nutritional status, such as weight loss and malnutrition, are a very common complication in patients with chronic obstructive pulmonary disease (COPD). These changes primarily affect the patients' quality of life and functional capacity and they are also independent prognostic indicators of both morbidity and mortality. Malnutrition in these patients is due to multiple factors including increases in resting energy expenditure, decreased food intake, the effects of certain drugs, and, perhaps most importantly, a high systemic inflammatory response. The present review covers the most important facets of the prevalence, etiology, pathogenesis, and consequences of malnutrition in COPD and considers which parameters for nutritional assessment are the most satisfactory for use in routine clinical practice. The strategy used to ensure correct nutritional status in these patients is also discussed.