Idiopathic interstitial pneumonias (IIPs) are diffuse lung diseases of unknown cause. Morbidity and mortality are high in patients with IIPs who have undergone lung resection. Postoperative acute exacerbation (PAE) of IIPs is one of the fatal complications after lung resection. From January 2001 to October 2009, 758 consecutive patients with lung cancer who had undergone lung resection at Tokyo Women's Medical University Hospital were investigated retrospectively. Forty (5.3%) of 758 patients had IIPs. PAE of IIPs was developed in 12 of the patients with IIPs. There were no significant differences in the age, gender, operation methods, histology, and pathological stage in the patients with or without PAE of IIPs. Three patients died of uncontrollable PAE of IIPs in hospital. The 30-day mortality of patients with PAE of IIPs in the last nine-year period has clearly decreased compared with the 30-day mortality of patients with PAE of IIPs between January 1996 and December 2000. PAE of IIPs causes high mortality. It is very difficult to predict the occurrence of PAE of IIPs. More efforts are required to develop strategies to prevent PAE of IIPs.