['Postoperative acute interstitial pneumonia is a subset of post-surgical acute respiratory distress syndrome (ARDS) and is responsible for one third of in-hospital deaths following lung resection in patients with primary lung cancer. We evaluated the usefulness of computed tomography (CT) for detection of interstitial pneumonia (IP) as a risk factor of postoperative ARDS.', 'Preoperative chest CT of patients who underwent thoracotomy for primary lung cancer was reviewed retrospectively and IP findings in the chest CT were detected.', 'A total of 1148 patients with primary lung cancer underwent thoracotomy. Fifteen patients (1.3%) developed postoperative ARDS. Eleven of these 15 patients died of ARDS. Three of 41 patients who received induction therapy developed postoperative ARDS. Induction therapy was a risk factor of postoperative ARDS (p<0.01). Eleven out of the 15 patients who developed postoperative ARDS had IP findings (10: localized, 1: diffuse) in their chest CT. Two of three patients who had postoperative ARDS after induction therapy also had IP findings. Chest CTs of 834 patients were retrospectively analyzed; 91 patients (10.9%) had IP-findings (diffuse 1.8%, localized 9.1%). Postoperative ARDS occurred in 8.8% of IP-positive patients, and in 0.4% of IP-negative patients (p<0.001).'] Is subclinical idiopathic pulmonary fibrosis also a risk factor of postoperative acute respiratory distress syndrome following thoracic surgery?