Clinical recurrence of Crohn's disease after surgical resection is a significant problem, with reported rates as high as 55% at 5 yr and 76% at 15 yr. Specific factors that predispose to postoperative recurrence of Crohn's disease have not been well defined. In addition, the underlying pathophysiology of recurrent disease and the reason for its localization to the neoterminal ileum are not well understood. Various operative techniques have been evaluated but none, aside from formation of an ostomy, has been shown to reduce the risk of recurrence. In contrast, there is increasing evidence that postoperative medical therapy has the potential to decrease the risk of postoperative recurrence. Historically, sulfasalazine may have a modest effect on reducing postoperative recurrence of ileal or ileocolonic disease. However, 5-ASA preparations that can selectively deliver mesalamine to the small bowel or anastomotic margin should be more effective. Indeed, in several studies and as confirmed by a meta-analysis, mesalamine has been demonstrated to reduce significantly postoperative recurrence of Crohn's disease. Metronidazole and 6-mercaptopurine or azathioprine also seem to be of benefit in postoperative prophylaxis of disease recurrence, but additional controlled studies are required to define better the efficacy and dose-response of these agents. Corticosteroids are ineffective at reducing postoperative recurrence.