Purpose: Our purpose was to evaluate F-18 FDG uptake in pulmonary lymphangitic carcinomatosis (PLC) according to CT findings and histology of lung cancer. Materials and Methods: Thirty-three lung cancer patients with PLC were enrolled in this retrospective study. All the patients had a CT-based diagnosis of PLC. Chest CT findings of PLC were classified on the basis of involvement of axial interstitium. We categorized the involvement of axial interstitium as group 1, and the involvement of peripheral interstitium only as group 2. Visual and semiquantitative analyses by F-18 FDG PET/CT were performed in the PLC lesions. At first, we analyzed the F-18 FDG uptake in the PLC by visual assessment. If abnormal uptake was seen in the PLC, we drew regions of interest in the PLC lesions to obtain the maximum SUVs (maxSUVs). Results: Of the 33 patients, 22 had abnormal F-18 FDG uptake in the visual assessment. There was no significant difference in the frequency of abnormal F-18 FDG uptake between group 1 and group 2 (p=0.17), although the frequency of group 1 tended to be higher than group 2 (15/19 (78.9%) in group 1, 7/14 (50.0%) in group 2). However, group 1 had a higher maxSUV than group 2 (p<0.01, group 1: 2.9¡¾1.4, group 2: 1.5¡¾0.6). There was no significant difference in the frequency of abnormal F-18 FDG uptake and maxSUV among the histology of the lung cancers. Conclusion: The involvement of axial interstitium in the PLC by lung cancer has a higher maxSUV than the involvement of only peripheral interstitium.