We aimed to explore lung cancer prevalence in interstitial lung disease (ILD) patients with or without connective tissue disorder (CTD) and idiopathic pulmonary fibrosis (IPF) in comparison with chronic obstructive pulmonary disorder (COPD).We evaluated lung cancer prevalence associated with ILD and IPF using Korean Health Insurance Review and Assessment Service (HIRA) data from January to December 2011. This database (HIRA-NPS-2011-0001) was sampled using random sampling of outpatients; 1,375,842 sample cases were collected, and 670,258 (age ≥ 40 ys) were evaluated. Patients with ILDs, IPF, CTD, or COPD were identified using the International Classification of Disease-10 diagnostic codes.Lung cancer prevalence rates per 100,000 persons for the sample population and those with ILD, IPF, CTD-ILD, and COPD were 420, 7334, 7404, 7272, and 4721, respectively. Lung cancer prevalence was significantly higher in those with ILD than in those with COPD (P < .01).More attention should be paid to lung cancer development in those with ILD as well as COPD.