A 55-year-old woman underwent simultaneous liver-kidney transplantation because of polycystic liver and kidney. Six months later, FDG PET/CT was acquired to evaluate possible lesions in the renal graft, which demonstrated abnormal F-FDG accumulation in the renal pelvic lesions without other abnormality. The subsequent pathology examination after biopsy demonstrated the polymorphic posttransplant lymphoproliferative disorders.