Aggressive fibromatosis or desmoid tumors, histologically indicated by small bundles of spindle cells in a fibrous background, are uncommon benign tumors without metastasis. They are recurrent and aggressive and their recurrence and severity is exacerbated following surgical operation. Based on previous reports, these tumors rarely present as intra-abdominal abscesses. Herein, a 54-year-old woman is presented who was referred with abdominal pain, fever, high ESR, and leukocytosis. On further evaluation, an intra-abdominal abscess was detected adjacent to splenic flexure of colon. Two months following antibiotic therapy, she carne back with the same clinical presentation. In CT-scan, an abdominal mass was detected. Based on a CT-guidedbiopsy, presence of mesenteric fibromatosis was reported. The patient underwent a surgical operation and the tumor was resected.