Acute exacerbations of chronic obstructive pulmonary disease occur often. Severity should be established by signs and symptoms and by reference to baseline pulmonary function test results when necessary. If the exacerbation is mild to moderate, treatment should include antibiotics, theophylline, beta agonists, and mucolytics. Severe exacerbations should be treated with these agents plus supplemental oxygen, intravenous corticosteroids, and, when appropriate, intubation and mechanical ventilation.