Patients with Crohn's disease (CD) could develop complications such as stricture, intestinal fistula and abdominal abscess. Some CD patients had poor response to medical therapy. The efficacy of exclusive enteral nutrition (EEN) to these adult active CD patients is still unclear. The investigators aim to study the efficacy of EEN in induction of remission in adult active CD patients with complications or poor response to drugs.

Active CD patients following up in our center who had been diagnosed as complicated disease with stricture, intestinal fistula, abdominal abscess and no response to drugs, were recruited since July 2013. Patients were only offered EEN for 12 weeks without using other drugs except that patients with abscess could use antibiotic therapy with or without percutaneous drainage. The disease activity was assessed by the Crohn's disease activity index (CDAI). CDAI<150 was taken as achieving clinical remission. Demographics and clinical variables were recorded. Nutritional (body mass index, albumin) and inflammatory (High sensitivity C-reactive protein and platelet) index were evaluated at baseline, week 4 and week 12. Some patients performed colonoscopy and/or computed tomography enterography (CTE) /resonance enterography(MRE) before and after EEN. Mucosal healing was assessed under endoscopy with SES-CD and the size of abscess was detected by CTE /MRE.

Inclusion Criteria:

1. >18 years old
2. Patients with CD was diagnosed clinically according to previously established international criteria [9]
3. The diagnosis of stricture, fistula and abdominal abscess was confirmed by ultrasound, CT enterography (CTE), and endoscopy. The bowel stricture should mainly cause by inflammation. Intolerance or failure to steroids or IFX was judged by medical history
4. The disease was in an active period.

Exclusion Criteria:

1. Intolerant to EEN or need emergency surgery
2. The bowel stricture should mainly cause by fibrosis

All consecutive adult active CD patients followed up in our center and had been diagnosed with disease complications including stricture, intestinal fistula, abdominal abscess or no response to drugs. Patients were recruited from July 2013 to July 2015.