Preventing Postoperative Relapse in Crohn's Disease Patients at Risk: Azathioprine Versus Mesalazine

Inclusion Criteria: * Signed informed consent, * Man or woman between 18 and 70 years of age, * Diagnosis of Crohn's disease confirmed by endoscopic and histological, or endoscopic and radiological criteria within one year or by histopathological criteria during resection, * Clinical remission defined as Crohn´s Disease Activity Index (CDAI) \< 200, within the last two weeks. No clinical relapse due to Crohn's disease since resection, * Moderate (i2a) or severe endoscopic recurrence (i3-i4) within 6 to 24 months after curative resection of the terminal ileum and partial colectomy with ileocolonic resection for complications of ileal Crohn´s disease and with a construction of an ileocolonic anastomosis, * Within the neoterminal ileum at least more than 5 aphthous lesions with normal mucosa between the lesions, or skip areas of larger lesions, * Negative pregnancy test at screening visit in females of childbearing potential, * Use of appropriate contraceptive methods for females of childbearing potential and males with procreative capacity during treatment and at least up to 3 months after the end of treatment. Exclusion Criteria: * Lesions confined to the ileocolonic anastomosis (i.e., \< 1 cm in length) * Short bowel syndrome, * Serious secondary illnesses of an acute or chronic nature, which in the opinion of the Investigator renders the patient unsuitable for inclusion into the study, * Serum creatinine levels exceeding 1.5 mg/dL or 130 umol/L, * Presence of an ileo-/col…