Purpose The aim of this study was to assess the diagnostic efficacy of PET/CT using various parameters for the characterization of adrenal nodules in lung cancer patients. Methods Sixty-one adrenal nodules in 51 lung cancer patients were evaluated. The final diagnosis was based on histology (n=2) or imaging follow-up (n=59, range of follow-up: 7-57 months, median 27 months). Each adrenal nodule was analyzed using four parameters of PET/CT: the maximum standardized uptake value ($SUV_{max}$), the adrenal nodule/liver ratio of the SUV (SUV ratio), Hounsfield units (HU) and size. The optimal cutoff of each parameter for the identification of metastatic nodule was determined by ROC analysis and then the diagnostic efficacy was compared among the parameters. Results Of the 61 adrenal nodules, 45 (73%) were considered metastasis. The optimal cutoff values of the parameters were $SUV_{max}$ >2.7, SUV ratio >1.3, HU >18 and size>20 mm, respectively. The sensitivity, specificity and accuracy by $SUV_{max}$ >2.7 were 88.9%, 87.5% and 88.5%, and those by SUV ratio >1.3 were 84.4%, 100% and 88.5%, respectively. The combination of SUV ratio >1.3 and HU >18 had sensitivity of 97.7%, specificity of 81.2% and accuracy of 93.4% to predict adrenal metastasis in patients with lung cancer. Conclusion SUV ratio from F-18 FDG PET/CT could identify the adrenal metastasis in lung cancer patients. The combination of SUV ratio and HU can improve the accuracy of differentiating benign and metastatic adrenal lesions in lung cancer patients.