Post operative recurrence (POR) is the rule in patients with Crohn’s disease (CD), mitigated with prophylactic therapy. The evidence for therapeutic choice and timing of intervention is lacking. We aimed to compare rates of POR in patients treated early with prophylactic 6-mercaptopurine (6-MP) or adalimumab. We conducted a prospective single center randomized open label clinical study, in which patients in surgical remission following their first ileocecectomy were randomized to receive early treatment with 6-MP or adalimumab. Patients were followed up clinically every 3 months and underwent endoscopy at weeks 32 and 58 post-operatively. The primary endpoint was endoscopic recurrence (ePOR) at 1 year (week 58), defined as a Rutgeerts score≥i2. We enrolled 35 patients (25 males, mean age 35±1.4 years, median disease duration 5±6.1 years) following ileocecectomy. Of these, 7(20%) were current smokers and 9(26%) biologics experienced. Patients allocated to adalimumab had significantly less ePOR than patients treated with 6MP at week 32 (21% vs 69%, p=0.004) and 58 (47% vs 75%), (p=0.03, HR=0.39, 95% CI=0.16-0.93). POR was associated with increased diameter of the resected small bowel surgical specimen, lower baseline body mass index (BMI), increased week 18 fecal calprotectin and serum alanine aminotransferase and decreased week 18 hemoglobin level. Adalimumab is more effective than 6-MP in preventing ePOR. Increased operative small bowel diameter and lower post-operative BMI were associated with ePOR. Eighteen weeks serum hemoglobin and ALT, and fecal calprotectin levels were predictive of endoscopic disease recurrence. (ClinicalTrials.gov ID NCT01629628).