Chronic obstructive pulmonary disease (COPD) is one of the most common lung disorders in adults and includes chronic bronchitis and emphysema. In COPD, the airway passages (known as bronchi and bronchioles) become obstructed because of inflammation and excess sputum (phlegm) production. With emphysema, the alveoli (tiny air sacs of the lung where oxygen is absorbed and carbon dioxide is released) are partially destroyed. These problems result in difficulty breathing and decreased amounts of oxygen delivered to the body's tissues. COPD affects between 12 million and 24 million persons and is a leading cause of death in the United States. COPD affects both men and women, and the most common cause is smoking (accounting for 80%-90% of cases). The September 26, 2012, issue of JAMA includes an article about COPD. This Patient Page is based on one previously published in the June 16, 2010, issue of JAMA.