The purpose of this study is to compare the effectiveness of weekly subcutaneously administered Methotrexate for maintaining relapse-free sustained steroid/Enteral Nutrition -free 1-year remission compared with:

• daily oral Azathioprine / 6 mercaptopurine in low risk paediatric Crohn's disease
• subcutaneously administered adalimumab in high risk paediatric Crohn's disease

In this randomized controlled trial PIBDNet (pediatric inflammatory bowel diseases network) aims to compare the following treatment strategy by dividing patients into two risk groups for aggressive disease evolution: the effectiveness of Methotrexate versus Azathioprine / 6 mercaptopurine for the maintenance of remission in Crohn's disease in children who are at low risk for aggressive disease and the effectiveness of Methotrexate versus adalimumab in the high risk group. PIBDNet hypothesizes that Methotrexate is superior to Azathioprine / 6 mercaptopurine for maintaining remission in Crohn's disease in the low risk strata and adalimumab is superior to Methotrexate in the high risk strata. In addition, the ancillary study is planned to analyse of Adalimumab treated patients from inclusion (TOP-Down) versus patients switched to Adalimumab due to failure of immunomodulator therapy (STEP-Up).

Inclusion Criteria:

1. Children 6-17, with a new-onset Crohn Disease diagnosed using established criteria (37, 38), requiring a steroid-based or Enteral nutrition based induction therapy

2. At initial diagnosis, wPCDAI >40 or CRP>2 times upper limit at diagnosis

3. all wPCDAI scores (0-120) are possible at inclusion (patients in remission and patients with active disease)

4. Luminal active Crohn Disease (B1) with or without B2 and/or B3 disease behavior

5. Initial exposure to 5-ASA and derivate is tolerated

6. Exposure to antibiotics is tolerated

7. If one of the following criteria is present, patients are allocated to the high risk group prior randomization:

   • Complex fistulizing perianal disease
   • Panenteric disease phenotype (defined as L3 with L4b per Paris classification or L3 with deep ulcers in duodenum, stomach or oesophagus (not HP (helicobacter pylori)- or NSAID-related))
   • Severe growth impairment (height z-score <-2 or crossing 2 percentiles or more) likely related to CD
   • Significant hypoalbuminemia (<30g/l), elevated C reactive protein (CRP) (at least 2 times above normal range), or wPCDAI >12.5 despite 3 weeks of optimized induction therapy with steroids or Exclusive enteral nutrition
   • B2, B3 or B2B3 disease behavior
   • Overall cumulative disease extend of ≥60 cm

8. Informed and signed consent

Exclusion Criteria:

1. Patients with wPCDAI<42,5 at initial diagnosis, except if CRP>2 times upper limit
2. No induction therapy with steroids or enteral nutrition
3. Previous therapy with any IBD (inflammatory bowel desease) -related medications other than induction therapy as detailed in this protocol (except 5-ASA).
4. Pregnancy or refusal to use contraceptives during the study period in pubertal patients (both boys and girls) unless absolute abstinence (no sexual activity) is confirmed at each study visit. Positive pregnancy testing throughout the study will trigger prompt withdrawal of the patient from the study.
5. Lactating mothers
6. Children with perianal fistulising disease who require surgical therapy (drainage, seton placement)
7. Patients homozygous for Thiopurine methyl transferase or those with Thiopurine methyl transferase activity <6 nmol/h/ml erythrocytes or <9nmol 6MTG (6 methylthioguanine/g Hb/h), unless they qualify as high risk patients
8. Evidence of un-drained and un-controlled abscess/phlegmon
9. Contraindication to any drugs used in the trial (including intolerance/hypersensitivity or allergy to either study drug (thiopurines, methotrexate or adalimumab))
10. Current or previous malignancy
11. Serious comorbidities (such as renal insufficiency, hepatitis, respiratory insufficiency) interfering with drug therapy or interpretation of outcome parameters or will make it unlikely that the patients will finish the trial.
12. Infection with mycobacterium tuberculosis
13. Moderate to severe heart failure (NYHA classe III/IV)
14. Oral anticoagulant therapy, anti-malaria therapy
15. Live vaccines exposure (including yellow fever) less than 3 weeks prior inclusion