Intraabdominal desmoid tumour or fibromatosis, recurrent but non-metastatic, invasive, fibroblastic proliferations, are rare tumours. From 1968 to 1989, 16 patients were treated at Gustave Roussy Institute. They were associated with familial adenomatous polyposis in 10% of cases. These tumours, observed mainly in young women (70 to 85% of cases), are aggravated by pregnancy, and spontaneous regression can occur at menopause, proving their hormonal dependence. Although histologically benign, they are serious lesions due to their invasive character; their excision is complete in only 50% of cases. They recur in 30% to 75% of cases and cause death of the patient in 30% of cases. Treatment is surgical but due to their often very slow course, and their spontaneous stabilisation in some cases, a mutilating surgical treatment (extensive small intestine resection) does not seem to be justified. Radiotherapy is effective only at doses incompatible with the site of these tumours (35 to 60 Gy). Chemotherapy has never been shown to be effective.