The role of inhaled corticosteroids (ICS) in chronic obstructive pulmonary disease (COPD) has been the subject of much controversy. Major international guidelines recommend selective use of ICS. Recently published meta-analyses have reported conflicting findings on the effects of inhaled steroid therapy in COPD. To determine the efficacy and safety of inhaled corticosteroids in stable patients with COPD, in terms of objective and subjective outcomes. A pre-defined search strategy was used to search the Cochrane Airways Group Specialised Register for relevant literature. Searches are current as of July 2011. We included randomised trials comparing any dose of any type of inhaled steroid with a placebo control in patients with COPD. Acute bronchodilator reversibility to short-term beta(2)-agonists and bronchial hyper-responsiveness were not exclusion criteria. The a priori primary outcome was change in lung function. We also analysed data on mortality, exacerbations, quality of life and symptoms, rescue bronchodilator use, exercise capacity, biomarkers and safety. Two review authors independently assessed trial quality and extracted data. We contacted study authors for additional information. We collected adverse effects information from the trials. Fifty-five primary studies with 16,154 participants met the inclusion criteria. Long-term use of ICS (more than six months) did not consistently reduce the rate of decline in forced expiratory volume in one second (FEV(1)) in COPD patients (generic inverse variance analysis: mean difference (MD) 5.80 mL/year with ICS over placebo, 95% confidence interval (CI) -0.28 to 11.88, 2333 participants; pooled means analysis: 6.88 mL/year, 95% CI 1.80 to 11.96, 4823 participants), although one major trial demonstrated a statistically significant difference. There was no statistically significant effect on mortality in COPD patients (odds ratio (OR) 0.98, 95% CI 0.83 to 1.16, 8390 participants). Long-term use of ICS reduced the mean rate of exacerbations in those studies where pooling of data was possible (generic inverse variance analysis: MD -0.26 exacerbations per patient per year, 95% CI -0.37 to -0.14, 2586 participants; pooled means analysis: MD -0.19 exacerbations per patient per year, 95% CI -0.30 to -0.08, 2253 participants). ICS slowed the rate of decline in quality of life, as measured by the St George's Respiratory Questionnaire (MD -1.22 units/year, 95% CI -1.83 to -0.60, 2507 participants). Response to ICS was not predicted by oral steroid response, bronchodilator reversibility or bronchial hyper-responsiveness in COPD patients. There was an increased risk of oropharyngeal candidiasis (OR 2.65, 95% CI 2.03 to 3.46, 5586 participants) and hoarseness. In the long-term studies, the rate of pneumonia was increased in the ICS group compared to placebo, in studies that reported pneumonia as an adverse event (OR 1.56, 95% CI 1.30 to 1.86, 6235 participants). The long-term studies that measured bone effects generally showed no major effect on fractures and bone mineral density over three years. Patients and clinicians should balance the potential benefits of inhaled steroids in COPD (reduced rate of exacerbations, reduced rate of decline in quality of life and possibly reduced rate of decline in FEV(1)) against the potential side effects (oropharyngeal candidiasis and hoarseness, and risk of pneumonia).