We determined the relationship between pulmonary fibrosis and lung cancer in the United States from 1979 through 1991 by analyzing death certificate reports compiled by the National Center for Health Statistics. Of the 26,866,600 people who died during the study period, 107,312 died with pulmonary fibrosis, 1,739,725 died with lung cancer, 2,040,634 died with chronic obstructive pulmonary disease, and 7,807 died with asbestosis. Lung cancer occurred less frequently among decedents with pulmonary fibrosis (4.81%) and more frequently among decedents with chronic obstructive pulmonary disease (10.06%) and decedents with asbestosis (26.60%) than among decedents in the general population (6.48%). We conclude that the prevalence of lung cancer among people who died with a diagnosis of pulmonary fibrosis is lower than the 10% to 40% prevalence that has been reported in case series of pulmonary fibrosis.