Interstitial lung diseases (ILDs) are associated with an increased risk of lung cancer, and pulmonary resection is well known to be associated with high postoperative morbidity and mortality in lung cancer patients. Postoperative mortality rate of acute exacerbation( AE) was reported 33.3~100%. Sex, CRP, KL-6, %vital capacity( VC), forced expiratory volume in 1 second( FEV1.0), history of AE, preoperative steroid use, and surgical procedures were identified as possible risk factors of AE in the univariate analyses by the data obtained from patients with non-small cell lung cancer who had undergone pulmonary resection and presented with a clinical diagnosis of ILD between January 2000 and December 2009 at 64 institutions throughout Japan. Multivariate analysis using these factors identified surgical procedures except for wedge resection, history of AE, KL-6, %VC, and male sex as independent risk factors. A score by risk prediction for AE was 5 X (history of AE)+4 X (CT:UIP pattern)+3 X (gender:male)+3 X (preoperative steroid use)+2 X (KL-6>1,000 U/ml)+1 X (VC≤80%). The predicted probability of risk score 15~22 is>0.25, and risk score 11~14 is 0.1~0.25. We can use a simple risk scoring system comprising seven parameters to identify high risk patients for AE, and provide essential information to support fair and objective clinical decision-making by thoracic surgeons.