Although weight loss is a common problem in chronic obstructive pulmonary disease (COPD), the precise cause of malnutrition in COPD patients is not known. The purpose of this study was to measure and compare resting energy expenditure (REE) in stable undernourished and adequately nourished COPD. REE was measured in normal, adequately nourished, and undernourished COPD patients by indirect calorimetry and then compared to predicted basal metabolic rate (BMR) calculated from the Harris‐Benedict equation. We found that measured REE, compared to predicted, was significantly higher in the undernourished group, (1.15 +/‐ 0.02) and compared to the adequately nourished COPD (0.99 +/‐ 0.03) and normal groups (0.93 +/‐ 0.02) (p less than 0.0001). We conclude that there is a hypermetabolic state in stable malnourished COPD patients which may be a factor in weight loss. This elevated REE also needs to be taken into account when determining caloric requirements for COPD patients.