The extracellular superoxide dismutase (SOD3, EC-SOD) enzyme is a major extracellular scavenger of the superoxide anion, a free radical with the potential to cause oxidative damage. Previously, R213G heterozygosity has been associated with a decreased risk of chronic obstructive pulmonary disease (COPD) and an increased risk of ischemic heart disease (IHD). We questioned whether SOD3 R213G homozygosity (213GG) influences morbidity, mortality, and lung function. We found 14 R213G homozygotes (213GG) among 95,871 individuals (1/7000) from the Copenhagen General Population Study and the Copenhagen City Heart Study. The hazard ratio for homozygotes versus noncarriers (NC) (213RR) was 2.8 (95% confidence interval: 1.2-6.8, p = 0.02) for IHD, 1.8 (0.7-4.8, p = 0.25) for any form of cancer, and 2.3 (0.9-6.2, p = 0.10) for all-cause mortality. R213G heterozygosity was not associated with morbidity or mortality. Among never-smokers, we found a 20% lower forced expiratory volume in 1 s (FEV1)% predicted (p = 0.003), a 16% lower FVC% predicted (p = 0.01), and a 7% lower FEV1/FVC ratio (p = 0.02) in R213G homozygotes compared to NC. Our results lead to the hypotheses that the SOD3 enzyme plays a role in cardiovascular disease and in impairing and maintaining lung function in never-smokers. However, our findings should be retested in larger studies and in nonsmoking COPD patient cohorts. Antioxid. Redox Signal. 24, 884-891.