 Chronic obstructive pulmonary disease COPD is a major public health issue with no curative treatment. In Switzerland estimated 5-7 of the total population are suffering from this chronic disease. According to current guidelines corticosteroids are part of treatment of acute exacerbations in COPD patients. Several studies suggest that corticosteroids accelerate the recovery of forced expiratory volume in 1 second FEV1, decrease duration of hospitalization, reduce treatment failure rate and improve clinical outcome. The additional therapeutic benefit on FEV1-recovery tough seems only to last for three to five days. The investigators recently published a hospital-based study showing that in patients presenting to emergency departments with acute exacerbation of COPD, a short five day treatment with systemic steroids was not inferior to a conventional 14 day treatment with regard to re-exacerbation. Cumulative corticosteroid dose could be reduced in this trial. To the investigators knowledge no data is available about the minimal necessary corticosteroid dose in an outpatient treatment setting so far. 