A limitation of our study was the small number of never-smokers. The histopathologic changes of RB can persist after cessation of smoking, but they often resolve.32 RB was found in all current smokers but only in 49% of ex-smokers. There is evidence that areas of GGO in proven RB-ILD cases decrease after smoking cessation.33 In all heavy smokers in the study by Nakanishi et al. the scores for the GGO and centrilobular nodules decreased significantly after smoking cessation, while those for linear-reticular opacity and emphysema were not changed. The smoking cessation had occurred 15–52 months before the follow-up HRCT study. Also in a longitudinal follow-up study of patients with smoker's lung GGO attenuation was reduced in those who had stopped smoking.34 On follow-up HRCT of patients with RB-ILD and DIP, areas of GGO showed resolution after smoking cessation and treatment.35, 36 The ex-smokers in the present study had stopped smoking 1–52 years before the HRCT imaging (mean 25.0); so, based on the results from previous studies, it is likely that the RB and GGO caused by previous active smoking had reduced or disappeared by the time of our study.