We report the case of a 36-year-old woman who previously underwent total thyroidectomy for papillary thyroid carcinoma. 18F FDG PET/CT images demonstrated multiple lymph nodes with increased FDG uptake in the neck, chest, and abdomen and diffusely increased FDG uptake in the spleen, which were highly suspicious findings for malignant lymphoma. However, subsequent biopsy of axillary lymph node presented reactive hyperplasia. Detailed history revealed that the patient had a history of generalized edema and severe arthralgia after contact with ginkgo nut one week ago. This case highlights allergic reaction mimicking lymphoma on FDG PET/CT.