Desmoid tumors are rare lesions with a local invasive potential and a risk of recurrence considered as benign due to the absence of metastases. They are included in fibromatoses and may be associated with Gardner's syndrome. The authors report an unusual case, in a 26 year old man, of a desmoid tumor invading ileon, right colon, appendix and the right ureter and responsible of a ureteral obstruction. Etiologic factors (traumatic, hormonal, auto-immune...) are discussed. The treatment of choice to lower the risk of recurrence is the complete surgical removal of the tumor.