The present study was performed to investigate the maximum standardized uptake value (SUVmax) in 2-[fluorine-18]-fluoro-2-deoxy-d-glucose (18F-FDG) positron emission tomography/computed tomography (PET/CT) to preoperatively distinguish invasive from less-invasive pulmonary adenocarcinoma.A total of 106 patients with resectable pulmonary adenocarcinoma (≤ 3 cm) who had undergone whole-body 18F-FDG PET/CT were enrolled. The SUVmax, diameter, and consolidation/tumor (C/T) ratio of the lung tumors were measured with 18F-FDG PET/CT and regional thin-section CT.Of the 106 patients, 32 had adenocarcinoma in situ (AIS), 13 had minimally invasive adenocarcinoma (MIA), and 61 had invasive adenocarcinoma (IAC). IAC lesions showed greater uptake of 18F-FDG, a larger tumor diameter, and greater C/T ratios than AIS and MIA (P < .001 for all). A multivariate analysis revealed that only the SUVmax, tumor diameter, and C/T ratio were independent risk factors for tumor invasiveness (P < .05 for all). The best cutoff values for the prediction of invasiveness were 2.15 for the SUVmax, 1.36 cm for the tumor diameter, and 0.36 for the C/T ratio. The SUVmax, tumor diameter, and C/T ratio showed similar predictive sensitivity (83.6%, 82.0%, and 88.5%, respectively). However, the SUVmax showed a greater predictive specificity than the C/T ratio (93.3% vs. 73.3%, respectively; P = .011) but similar to that of the tumor diameter. The predictive sensitivity and specificity were not improved using the 3 combined parameters compared with SUVmax alone.The present study has demonstrated that the SUVmax is a good preoperative predictor for the invasiveness of pulmonary adenocarcinoma (≤ 3 cm). It will help surgeons plan low invasive treatment of preinvasive tumors.