There are several reports describing [18F] fluorodeoxyglucose positron emission tomography (FDG-PET) findings in patients with lymphomatoid granulomatosis (LYG). We report a case of grade I LYG that showed increased uptake of FDG. The patient was a 63-year-old Japanese male who underwent an FDG-PET/computed tomography (CT) scan in screening for a malignant lesion. Increased uptake of FDG [maximum standard uptake value (SUV(max)), 3.7] was observed in the right hilar region in FDG-PET and enhanced CT revealed a round, abnormal mass that also showed increased FDG uptake. The patient had no previous symptoms. A tumor biopsy was performed and the histological diagnosis was grade I LYG. Therefore, increased SUV(max) in FDG-PET might be useful for diagnosing of LYG.