To investigate the relationship between air pollution and female lung cancer, the authors conducted a matched case-control study using female deaths that occurred in Taiwan from 1994 through 2003. Data on all eligible female lung cancer deaths were obtained from the Bureau of Vital Statistics of the Taiwan Provincial Department of Health. The control group consisted of women who died from causes other than cancer or diseases associated with respiratory problems. The controls were pair matched to the cases by sex, year of birth, and year of death. Each matched control was selected randomly from the set of possible controls for each case. A municipality-based aggregate index of long-term exposure to air pollution was created by dividing the annual average of the measured values for each pollutant by the National Ambient Air Quality Standard for that pollutant. The ratios for each pollutant were scaled to a 100-point scale and then averaged together to generate an index value representing the net burden of these pollutants, with each weighted equally. The subjects were divided into tertiles according to the levels of the index just described. Women who lived in the group of municipalities with highest levels of air pollution exposure index were at a statistically significant increased lung cancer risk compared to the group living in municipalities with the lowest air pollution exposure index after controlling for possible confounders (OR = 1.28, 95% CI = 1.02-1.61). The findings of this study warrant further investigation of the role of air pollutants in the etiology of lung cancer.