BACKGROUND/AIMS: New lesions recur within weeks to months after ileal resection and ileocolonic anastomosis for Crohn's ileitis. A double-blind controlled trial was performed using metronidazole to prevent recurrence after ileal resection. METHODS: Sixty patients who underwent curative ileal resection and primary anastomosis were included within 1 week after surgery. Thirty patients received metronidazole (20 mg/kg body wt) daily for 3 months, and 30 patients received placebo. Treatment was then discontinued. Nine patients dropped out during treatment, 7 in the metronidazole group and 2 in the placebo arm. RESULTS: At 12 weeks, 21 of 28 patients (75%) in the placebo group had recurrent lesions in the neoterminal ileum as compared with 12 of 23 patients (52%) in the metronidazole group (P = 0.09). The incidence of severe endoscopic recurrence was significantly reduced by metronidazole (3 of 23; 13%) as compared with placebo (12 of 28; 43%; P = 0.02). Patients in the metronidazole arm had more frequent side effects. Metronidazole therapy statistically reduced the clinical recurrence rates at 1 year (4% vs. 25%). Reductions at 2 years (26% vs. 43%) and 3 years (30% vs. 50%) were not significant. CONCLUSIONS: Metronidazole therapy for 3 months decreases the severity of early recurrence of Crohn's disease in the neoterminal ileum after resection and seems to delay symptomatic recurrence.