A 44-year-old man with advanced follicular lymphoma received 8 cycles of chemotherapy, which resulted in the complete disappearance of the original disease. However, a new abdominal mass with positive (18)F-FDG PET/CT uptake appeared after 5 cycles and this was maintained until 3 weeks after the completion of 8 cycles. Open biopsy showed a benign mass with fat necrosis. Although PET/CT is useful in evaluating residual lymphoma after chemotherapy, various benign conditions such as a result of post-chemotherapy inflammation, even in new locations without prior disease, should be noted as causes of false positive uptake.