OBJECTIVE The purpose of this study was to evaluate the accuracy of 3'-deoxy-3'-F-fluorothymidine (FLT) positron emission tomography (PET) for detection of lung tumor in comparison with 2-deoxy-2-F-fluoro-D-glucose (FDG) PET. METHODS Fifty-four patients with newly diagnosed pulmonary nodules on chest computed tomographic (CT) scan suggestive of a malignant tumor were examined with both FLT and FDG PET. The intensity of uptake in lung tumors was scored. For visualized lesions, the maximum standardized uptake value (SUV) was calculated. RESULTS Thirty-six patients were found to have lung cancer; and 18, benign lesions. Using visual analysis, the sensitivity of FLT PET for detection of lung cancer was 83%; the specificity, 83%; and the accuracy, 83%. The corresponding values for FDG PET were 97%, 50%, and 81%, respectively. The specificity of FLT PET was significantly higher than that of FDG PET. The uptake of FLT in lung cancer was significantly lower than that of FDG. Using semiquantitative analysis, the sensitivity of FLT was 86%; the specificity, 72%; and the accuracy, 81%. The corresponding values for FDG were 89%, 67%, and 81%, respectively. CONCLUSIONS These preliminary results indicate that FLT PET may be specific for malignant tumors although uptake of FLT in lung cancer was significantly lower than that of FDG.