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RATIONALE: Idiopathic interstitial pneumonia is characterized by pulmonary fibrosis and high mortality. OBJECTIVES: We examined the association between ever-diagnosed venous thromboembolism and risk of incident idiopathic interstitial pneumonia. Venous thromboembolism was taken as a proxy for a procoagulant state in an individual. METHODS: We conducted a study of the entire Danish population from 1980 through 2007, comprising 7.4 million individuals. Incident idiopathic interstitial pneumonia, ever-diagnosed venous thromboembolism, and use of prescription anticoagulants were drawn from national Danish registries. MEASUREMENTS AND MAIN RESULTS: Age-standardized incidence rates per 10,000 person-years for idiopathic interstitial pneumonia were higher among those ever diagnosed with venous thromboembolism (1.8; n = 158,676), pulmonary embolism (2.8; n = 70,586), and deep venous thrombosis only (1.2; n = 88,090), than among control subjects (0.8; n = 7,260,278). Multivariate-adjusted hazard ratios for idiopathic interstitial pneumonia were 1.8 (95% confidence interval [CI], 1.7-1.9) in those ever diagnosed with venous thromboembolism, 2.4 (95% CI, 2.3-2.6) in those ever diagnosed with pulmonary embolism, and 1.3 (95% CI, 1.2-1.4) in those ever diagnosed with deep venous thrombosis only, compared with control subjects. Corresponding hazard ratios in those ever diagnosed with venous thromboembolism stratified in those ever and never treated with anticoagulants were 1.4 (95% CI, 1.2-1.6) and 2.8 (95% CI, 2.4-3.1) (venous thromboembolism x anticoagulation use interaction on idiopathic interstitial pneumonia outcome: P = 1.5 x 10(-10)). CONCLUSIONS: In the general population, ever-diagnosed venous thromboembolism was associated with idiopathic interstitial pneumonia, particularly among those never treated with anticoagulants. [ABSTRACT FROM AUTHOR]