The current report presents a case of an omental fibromatosis discovered incidentally in a 46-year-old woman with no particular medical history and few symptoms. A surgical biopsy was performed initially, and microscopic examination revealed myofibroblastic proliferation. After additional immunohistochemical and molecular analyses, omental fibromatosis was diagnosed. Omental fibromatosis, also called intra-abdominal desmoid, is a rare and benign tumour but can be locally aggressive. Majority of cases are asymptomatic, and difficult to diagnose based on clinical presentation and radiological investigation. Final diagnosis is usually made on histopathology and immunohistochemistry studies. Surgical wide excision is currently the treatment of choice.