Medical therapies for Crohn’s disease (CD) range from the relatively benign and less effective (5-aminosalicylates and antibiotics) to the more toxic but more effective (steroids, immunomodulators, and anti-tumour necrosis factor antibodies). Despite such treatments about 80% of patients need surgery within 20 years of diagnosis and 20–40% within three years. Earlier more aggressive medical treatment might reduce rates of surgery but better methods of assessing prognosis are needed so that early effective but potentially toxic treatments can be reserved for …