BACKGROUND Low body weight in patients with chronic obstructive pulmonary disease (COPD) is associated with an impaired pulmonary status, reduced diaphragmatic mass, lower exercise capacity and higher mortality rate when compared to adequately nourished individuals with this disease. Nutritional support may therefore be a useful part of their comprehensive care. OBJECTIVES To conduct a systematic review of randomized controlled trials (RCTs) to clarify whether nutritional supplementation (caloric supplementation for at least 2 weeks) improved anthropometric measures, pulmonary function, respiratory muscle strength and functional exercise capacity in patients with stable COPD. SEARCH STRATEGY Randomized controlled trials (RCTs) were identified from the Cochrane Airways Group register of RCTs, a hand-search of abstracts presented at international meetings and consultation with experts. SELECTION CRITERIA Two reviewers independently selected trials for inclusion, assessed quality and extracted the data. DATA COLLECTION AND ANALYSIS Within each trial and for each outcome, we calculated an effect size. The effect sizes were then pooled by a random-effects model. Homogeneity among the effect sizes was also tested. MAIN RESULTS From 272 references, nine RCTs were ultimately included. Six papers were considered as high quality and only two studies were double-blinded. For each of the outcomes studied, the effect of nutritional support was small: the 95% confidence intervals around the pooled effect sizes all included zero. The effect of nutritional support was homogeneous across studies. An additional search conducted in August 2001 did not identify further studies. REVIEWER'S CONCLUSIONS Nutritional support had no significant effect on anthropometric measures, lung function or exercise capacity in patients with stable COPD.