The association between severe nutritional depletion and chronic obstructive pulmonary disease (COPD) has long been recognized. A potential therapeutic benefit to nutritional support was previously suggested by us in a pilot investigation. Subsequent studies have reported conflicting results regarding the role of nutritional therapy in this clinical population. We report a randomized controlled study of nutritional therapy in underweight patients with COPD that combines an initial inpatient investigation (controlled nutritional support) with a prolonged outpatient follow-up interval. Provision of adequate calorie and protein support, adjusted to metabolic requirements, resulted in weight gain (intervention = +2.4 kg versus control -0.5 kg), improved handgrip strength (intervention = +5.5 kg-force versus control -6.0 kg-force), expiratory muscle strength (intervention = +14.9 cm H2O versus control -9.2 cm H2O), and walking distance (intervention = +429 feet versus control -1.0 foot). Inspiratory muscle strength was also improved (intervention = +11.4 cm H2O versus control +4.8 cm H2O) although this did not quite reach statistical significance. We conclude that provision of adequate nutrient supply under controlled conditions results in significant clinical improvements in the COPD patient population. However, the intervention is costly, time-intensive, and of limited therapeutic magnitude. More detailed work of alternative outpatient strategies combined with additional rehabilitative measures is indicated to delineate the full therapeutic potential of nutritional support for this clinical population.