Chronic obstructive pulmonary disease (COPD) is a major public health problem worldwide. COPD is strongly related to cigarette smoke exposure, but not all smokers develop the disease. It is thought that COPD progresses slowly over time stimulated by environmental exposures, including free radicals from cigarette smoke, which ultimately establish chronic inflammation and result in a progressive destruction of lung tissues. COPD is known to occur in family clusters, which has prompted interest in determining genetic risk factors for the disease. Several genetic studies have identified an association between extracellular superoxide dismutase (ECSOD) polymorphisms and risk for developing COPD. ECSOD is an antioxidant protein that scavenges superoxide free radicals from cigarette smoke and protects the lungs from free radical damage and chronic inflammation.