BACKGROUND Recent studies have revealed a potential relationship between the presence of ground glass opacity (GGO) on regular computerized tomography (CT) and adenocarcinomas. OBJECTIVE To investigate features of pre-invasive lung adenocarcinoma lesions on thin-section CT. METHODS We evaluated 59 cases of atypical adenomatous hyperplasia (AAH) and 35 cases of adenoma in situ (AIS) confirmed by histopathology. Comparison of thin-section CT features, such as size, shape, margin, internal characteristics, and adjacent structures of pre-invasive lesions were analyzed. Lesions were further classified to pure ground glass opacity (pGGO) and mixed ground glass opacity (mGGO). Differences were analyzed using Chi-square or Fisher tests. RESULTS There were significant differences in lobulation, spiculation, and bubble lucency between pGGO and mGGO (P < 0.05), while no differences in air bronchogram, pleural indentation, or vascular morphological changes were identified (P > 0.05). In the group of pGGO, AAH and AIS lesions did not differ significantly in size (P > 0.05), while significant differences were found with respect to lobulation, spiculation, pleural indentation, and vascular morphological changes (P < 0.05). In the group of mGGO, AAH and AIS lesions were significantly different with respect to size (P < 0.05), while no differences were found in lobulation, spiculation, bubble lucency, air bronchogram, or pleural indentation (P > 0.05). Only vascular morphological changes were significantly different between AAH and AIS lesions (P < 0.05). CONCLUSIONS The features of thin-slice CT of AAH and AIS reflected the corresponding morphological changes from AAH progressing to AIS or adenocarcinoma.