Chronic obstructive pulmonary disease (COPD) is an increasingly important health problem world-wide. Whereas most other leading diseases have shown a decline in the past decades, COPD morbidity and mortality is on a steady increase. Exacerbations are usually defined as an increase in cough, a change in the colour or quantity of sputum, and a worsening dyspnea. The role of bacterial infections and the efficacy of antimicrobial therapy in acute exacerbations of chronic bronchitis (AECD) is still controversial. Exacerbations of chronic bronchitis are a common occurrence in clinical practice and are a leading cause of antibiotic prescription among respiratory infections. It is still uncertain whether each new exacerbation may deteriorate the natural history of chronic bronchitis. Undoubtedly, every episode includes a temporary worsening in lung function and may therefore pose the threat of respiratory failure or death in more severely obstructed patients.