Background: Previous studies have reported a high prevalence of lung cancer in patients with idiopathic pulmonary fibrosis (IPF), ranging from 8% to 48%. However, there are few papers which report the outcomes of anticancer treatment in this cohort. Methods: This retrospective study was conducted using prospectively collected cohort of IPF patients between May 2002 and April 2011. During 9-year period, 1105 patients with IPF were prospectively collected, and 204 patients with IPF and lung cancer were enrolled in this study. Results: Of the 204 patients, 89 (44%) were diagnosed with lung cancer during 2.5 (IQR, 1.5-4.9) years of follow-up period with IPF, while 115 (56%) were diagnosed with IPF and lung cancer at the same time. Squamous cell carcinoma (35%) and adenocarcinoma (34%) were most frequent types. Eighty five (78%) patients underwent definitive surgery among 109 patients of the surgically operable stage (clinical stage I to IIIa). Treatment-related complications, such as acute exacerbation and pneumonia, were occurred in 33/85 (39%), 28/90 (31%), 6/39 (15%), and 9/19 (47%) cases after surgical lung resection, chemotherapy, radiation therapy, and combined chemoradiation therapy, respectively. The overall mortality of these complications was 71% (54/76). Conclusions: The present study showed high incidence and high mortality of complications to anticancer treatment of lung cancer in patients with IPF. Therefore, careful assessment to both IPF and lung cancer is required, and further studies are needed to improve the outcome of treatment-related complications.