Exacerbations of chronic obstructive pulmonary disease (COPD) are associated with worse health and increased healthcare utilisation. The Inhaled Steroids in Obstructive Lung Disease in Europe (ISOLDE) study in COPD showed a 26% reduction in the yearly rate of exacerbations in patients treated with fluticasone propionate (FP) compared to placebo, but did not indicate which patients showed greatest benefit. In this study the patients were stratified into mild and moderate-to-severe COPD using the American Thoracic Society criterion of forced expiratory volume in one second (FEV1) 50% predicted, and the total number of exacerbations and those requiring treatment with oral corticosteroids were examined. There were 391 (195 FP) patients with mild COPD and 359 (180 FP) patients with moderate-to-severe disease. The exacerbation rate was highly skewed in mild disease, but more normally distributed in moderate-to-severe disease. FP reduced the overall exacerbation rate in moderate-to-severe disease (FP median rate 1.47 yr(-1), placebo 1.75 yr(-1)), but not in mild disease (FP 0.67 yr(-1), placebo 0.92 yr(-1)). FP use was associated with fewer patients with > or = 1 exacerbation x yr(-1) being treated with oral corticosteroids (mild: FP 8%, placebo 16%; moderate-to-severe: FP 17%, placebo 30%). Effects of fluticasone propionate on exacerbations were seen predominantly in patients with a postbronchodilator forced expiratory volume in one second <50% predicted. These data support recommendations in the Global Initiative for Chronic Obstructive Disease treatment guidelines that inhaled corticosteroids should be considered in patients with moderate-to-severe chronic obstructive pulmonary disease who experience recurrent exacerbations.