The authors report a case of perineal Crohn disease with three anal fissures. Because of a persistant fever without any clinical aspect of abscess they practiced MRI examination that discovered an abscess of the recto-vaginal wall. The patient was operated under general anaesthesia. This clinical case shows the interest of radiologic exams, particularly pelvic MRI for the precise lesional diagnosis of anoperineal lesions of Crohn's disease, that is still complex and difficult to treat.