A 39-year-old woman received an intrauterine device (IUD) placement 6 years ago, and lower abdominal pain occurred intermittently 1 year after the placement. Every attack lasted for a few days and was relieved spontaneously. Pain occurred again 2 days before admission, with nausea, vomiting, and constipation. Physical examination revealed a mass in the left lower abdomen with localized tenderness. Abdominal computed tomography showed that a mass, 5.9 × 4.0 cm in size, was adjacent to the aorta abdominalis and below the umbilicus. A 2-cm circinate foreign body was observed close to the mass (Figure 1). Exploratory laparotomy showed that a metallic IUD was on the mesenterium, while the uterine was intact, and the mesenterium, 130 cm distal to the Treitz ligament until 40 cm proximal to the ileocecum, was occupied by purple nodules, which coalesced into a large mass (Figure 2). Diseased mesenterium and relevant intact small bowel were resected successfully. Postoperative pathologic study showed abnormal crowding of follicles and many large centroblasts with nucleoli adjacent to the nuclear membrane with admixed cleaved cells, in accordance with Grade III follicular lymphoma (Figure 3). Immunohistochemistry results were positive for CD20, CD21, mum-1, Bcl-2, and Bcl-6 and weakly positive for CD10, with a Ki-67 index of 60%. Further bone marrow smear and biopsy had negative results. She was treated with 6 cycles of combined chemotherapy after surgery, and no relapse was observed at the 1-year follow-up. Informed consent was obtained.