Background Chronic obstructive pulmonary disease (COPD) is a major public health issue affecting approximately four to seven percent of the Swiss population. According to current inpatient guidelines, systemic corticosteroids are important in the treatment of acute COPD exacerbations and should be given for five to seven days. Several studies suggest that corticosteroids accelerate the recovery of the FEV1 (forced expiratory volume in one second), enhance oxygenation, decrease duration of hospitalization and improve clinical outcome. However, the additional therapeutic benefit on FEV1 recovery appears to be most apparent in the first three to five days. No data are available on the minimal necessary corticosteroid dose and treatment duration in primary care patients with acute COPD exacerbations. Given that many COPD patients are treated on an outpatient basis, there is an urgent need to improve evidence about COPD management in this setting. The aim of this study is to investigate whether a three-day treatment with orally administered corticosteroids is non-inferior to a five-day treatment in acute exacerbations of COPD in a primary care setting. Methods The proposed study is a prospective, double-blind, randomized controlled trial conducted in a primary care setting, including an anticipated number of 470 patients with acutely exacerbated COPD. Participants are randomised to receive systemic corticosteroid treatment of 40 mg prednisone daily for five days (conventional arm, n = 235), or for three days, followed by two days of placebo (experimental arm, n = 235). Antibiotic treatment for seven days is given to all patients with CRP ≥ 50 mg/l, known diagnosis of bronchiectasis, or presenting with Anthonisen Type-I exacerbation. Additional treatment after inclusion is left at the discretion of the treating general practitioner. Follow-up visits are performed on days three and seven by the treating general practitioners, followed by telephone interviews on days 30, 90 and 180 after inclusion into the study. Primary endpoint is the time to next exacerbation during a six-months follow-up period, which includes re-exacerbation during index exacerbation. Discussion This study is designed to assess whether a three-day course of corticosteroid treatment is not inferior to the current conventional five-day treatment course in outpatients with exacerbated COPD regarding time to next exacerbation. Depending on the results, this trial might lead to a further reduction of cumulative corticosteroid dose in COPD patients.