Recurrence of Crohn's disease (CD) lesions in the neo-ileum after apparently curative resection frequently occurs after surgery. The most appropriate prophylactic treatment has not been clearly defined. This study evaluated the efficacy of 5-ASA and azathioprine in decreasing postoperative recurrence and analysed the presence of variables associated with recurrence. Thirty-nine patients (mean age 32.8 years, range 18-61) with a history of ileal or ileocecal surgical resection were studied. They received 5-ASA (3 mg/day) or azathioprine (50 mg/day) immediately after the operation and for 2 years thereafter. Patients were followed clinically (Crohn's disease activity index) and serologically every 3 months and by imaging methods every 6 months. The latter included colonoscopy with ileoscopy and if not available, small bowel barium or ultrasonographic study. Laboratory tests included ESR, C-reactive protein, white blood cell and platelet count, fibrinogen and albumin. The end-point evaluated included clinical recurrence (CR), serological recurrence (SR: alteration of at least three of the above-mentioned variables) and morphologic recurrence (MR: endoscopic recurrence > 1 according to Rutgeerts score or radiological or ultrasonographic recurrence). Eighteen patients received azathioprine and 21 received 5-ASA. Thirty-four patients were evaluated. The cumulative proportion of patients with recurrence was 29% (CR), 35% (SR) and 50% (MR). Statistical analysis did not show significant differences between the two groups. Twenty-seven patients completed the 2-year study (11 in the azathioprine group and 16 in the 5-ASA group). Crude relapse rates were 37% (CR), 44% (SR) and 69% (MR) in the 5-ASA group and 36% (CR), 45% (SR) and 64% (MR) in the azathioprine group. No statistically significant differences were observed between groups. No variables associated with recurrence were detected. In conclusion, treatment does not prevent a high percentage of postsurgical recurrence. 5-ASA (3 g/day) and azathioprine (50 mg/day) showed similar efficacy in the prevention of recurrence.