Objective: To retrospectively compare focal interstitial fibrosis(FIF),atypical adenomatous hyperplasia(AAH),adenocarcinoma in situ(AIS),and minimally invasive adenocarcinoma(MIA)with pure ground-glass opacity(GGO)using thin-section computed tomography(CT).Materials and Methods: Sixty pathologically confirmed cases were reviewed including 7 cases of FIF,17 of AAH,23of AIS,and 13 of MIA.All nodules kept pure ground glass appearances before surgical resection and their last time of thin-section CT imaging data before operation were collected.Differences of patient demographics and CT features were compared among these four types of lesions.Results: FIF occurred more frequently in males and smokers while the others occurred more frequently in female nonsmokers.Nodule size was significant larger in MIA(P < 0.001,cut-off value = 7.5 mm).Nodule shape(P = 0.045),margin characteristics(P < 0.001),the presence of pleural indentation(P = 0.032),and vascular ingress(P < 0.001)were significant factors that differentiated the 4 groups.A concave margin was only demonstrated in a high proportion of FIF at 85.7%(P = 0.002).There were no significant differences(all P > 0.05)in age,malignant history,attenuation value,location,and presence of bubble-like lucency.Conclusion: A nodule size > 7.5 mm increases the possibility of MIA.A concave margin could be useful for differentiation of FIF from the other malignant or pre-malignant GGO nodules.The presence of spiculation or pleural indentation may preclude the diagnosis of AAH.