Our objective is to study the prophylactic effect of Vitamin D3 to prevent post-operative recurrence of Crohn's disease (CD), with an endoscopic endpoint 6 months after surgery as the primary outcome. Endoscopy has been an established surrogate marker for future clinical relapse. Secondary objectives include clinical recurrence rates at 6 months, the difference in recurrence rates among patients with and without low Vitamin D levels at baseline, the effects of Vitamin D3 on quality of life parameters, resource use and related costs.