BackgroundPrimary visceral malignant fibrous histiocytoma (MFH) is a rare disease, and few cases have been reported in the English literature. However, retained foreign bodies in the abdomen after surgical procedures are important causes of intra-abdominal infections. For legal and ethical reasons, there are few publications in the literature. In this article, we describe for the first time a case of malign abdominal fibrous histiocytoma associated with a surgical sponge forgotten in the abdominal cavity a long time ago.Case presentationA 64-year-old male presented to our surgical department with cachexia, abdominal pain, distention and pyrexia of unknown origin. He had a medical history of abdominal surgery for peptic ulcer perforation 32 years ago. Clinical examination revealed fever with a distended and painful abdominal wall. Radiological imaging of the abdomen showed multiple heterogeneous masses in one large cystic cavityalmost completely filling the abdomen. The patient underwent a laparotomy, and interestingly, opening the cyst revealed retained surgical gauze (RSG). The origin of the tumor was the visceral peritoneum, and it was excised totally.ConclusionsPrimary intra-abdominal MFH can present as a complication of long-lasting RSG. Therefore, clinicians must remember this while establishing the differential diagnosis for patients with a history of previous abdominal surgery and presenting with symptoms associated with both the tumor and systemic inflammatory response.