In this case control study, cases were ascertained at the multiple collaborating centers and controls were identified by telephone screening. A telephone interview was conducted to collect information needed to test hypotheses concerning cigarette smoking, occupational exposure, indoor exposures, other environmental factors, and host factors. To limit disease misclassification, two pathologists experienced with interstitial diseases of the lung reviewed histopathological material from all cases to exclude entities other than interstitial lung fibrosis and to fully characterize the cases clinically. The mortality of this large series of cases was also described.