A 64-year-old man underwent initial F-FDG PET/CT staging for gastric cardia adenocarcinoma, which showed the primary gastric tumor, several bone metastases, and high uptake in a periurethral mass mimicking pelvic neoplasm developed after injection of polydimethylsiloxane (Macroplastique) urethral bulking agent 6 years ago for postprostatectomy stress urinary incontinence. This case showed a very rare complication of silicon particle injection therapy, and the intense uptake is likely due to granulomatous reaction around the implant.