The evidential support for antimicrobial therapy of AECB is very limited. Hence, the indication for antibiotic treatment for AECB should be made very discriminatingly. For outpatients, the criteria for the indication are met when COPD is moderate to severe and all three symptoms for an exacerbation are present (increased sputum production, increased sputum purulence and increased dyspnoea), when exacerbations recur frequently or when there is cardiac comorbidity. The choice of the antibiotic is based on the severity of the COPD, the expected frequency of recurrence, risk factors for treatment failure, a recent antibiotic therapy and microbiological evidence of pathological organisms.